Building from source is not easy if something is a bit different, and I had a hard time with some directory and configuration options. I was floundering around the web until I found this site that translated from Chinese. No one else had the solution.  I couldn't get php fpm to start until I changed the directory (Item 2.ERROR: Unable to globalize). I had other issues listed but I was able to solve them. Please don't delete this, it is very useful info.

The original site  (it is in Chinese, not my site, but I want to give credit):

(there is some more there, you can goto the site)

blog.dream1987.top/?paged=2

Installation problems:

1. configure: error:. Xml2-config not found Please check your libxml2 installation.

solution:

apt-get install libxml2-dev

 

2.Warning: Declaration of PEAR_Installer :: download () should be compatible with & PEAR_Downloader :: download ($ params) in phar: ///root/php-7.0.0alpha1/pear/install-pear-nozlib.phar/PEAR /Installer.php on line 43

Warning: Declaration of PEAR_PackageFile_Parser_v2 :: parse () should be compatible with PEAR_XMLParser :: parse ($ data) in phar: ///root/php-7.0.0alpha1/pear/install-pear-nozlib.phar/PEAR/PackageFile/ Parser / v2.php on line 113 
[PEAR] Archive_Tar - already installed: 1.3.13 
[PEAR] Console_Getopt - already installed: 1.3.1 
[PEAR] Structures_Graph- already installed: 1.0.4

Warning: Declaration of PEAR_Task_Replace :: init () should be compatible with PEAR_Task_Common :: init ($ xml, $ fileAttributes, $ lastVersion) in phar: ///root/php-7.0.0alpha1/pear/install-pear-nozlib. phar / PEAR / Task / Replace.php on line 31 
[PEAR] XML_Util - already installed: 1.2.3

Warning: Declaration of PEAR_Task_Windowseol :: init () should be compatible with PEAR_Task_Common :: init ($ xml, $ fileAttributes, $ lastVersion) in phar: ///root/php-7.0.0alpha1/pear/install-pear-nozlib. phar / PEAR / Task / Windowseol.php on line 76

Warning: Declaration of PEAR_Task_Unixeol :: init () should be compatible with PEAR_Task_Common :: init ($ xml, $ fileAttributes, $ lastVersion) in phar: ///root/php-7.0.0alpha1/pear/install-pear-nozlib. phar / PEAR / Task / Unixeol.php on line 76 
[PEAR] PEAR - already installed: 1.9.5

solution:

Workaround not found (http://pear.php.net/bugs/bug.php?id=20554)

3. Start php-fpm

1.ERROR: failed to open configuration file '/usr/local/etc/php-fpm.conf': No such file or directory (2) 
ERROR: failed to load configuration file '/usr/local/etc/php-fpm.conf' 
ERROR: FPM initialization failed

solution:

Php-fpm.conf copy files from the source file to that location.

cp /root/php-7.0.0alpha1/sapi/fpm/php-fpm.conf /usr/local/etc/php-fpm.conf

2.ERROR: Unable to globalize '/usr/local/NONE/etc/php-fpm.d/*.conf' (ret = 2) from /usr/local/etc/php-fpm.conf at line 125. 
ERROR: failed to load configuration file '/usr/local/etc/php-fpm.conf' 
ERROR: FPM initialization failed

solution:

Edit /usr/local/etc/php-fpm.conf document introduced * .conf part, change to the correct path include = / usr / local / etc / php-fpm.d / *. Conf

If there is no /usr/local/etc/php-fpm.d directory, create the directory.

3.WARNING: Nothing matches the include pattern '/usr/local/etc/php-fpm.d/*.conf' from /usr/local/etc/php-fpm.conf at line 125. 
ERROR:. No pool defined at least one pool section must be specified in config file 
ERROR: failed to post process the configuration 
ERROR: FPM initialization failed

solution:

cp www.conf.default www.conf

4.ERROR: [pool www] can not get gid for group 'nobody' 
ERROR: FPM initialization failed

solution:

Www.conf open files, user and group users into nginx default settings, usually the default is www-data.

To maximize the server performance with highest speed, with fewest resources, i have decided to compile PHP 8 manually from minimal Linux/Unix-based OS (my Linux distro is rpm-based packages) 

My system has successfully powered up by PHP 8.0.9 - with Opcache/JIT enabled & other several PHP extension module. Here is several experience that may save you several hours of research.

1. Before step (3) - Configure and build PHP - to ensure that no errors occurs, you can refer to my prerequisites library. 

sudo dnf install \
gcc gcc-c++ make cmake autoconfig \
zlib zlib-devel pcre pcre-devel \
libxml2-devel libxslt-devel \
bzip2-devel curl-devel libzip-devel\
sqlite-devel \
systemd-devel \
openssl-devel \
libffi-devel \
libpng libpng-devel libwebp libwebp-devel libjpeg libjpeg-devel libXpm libXpm-devel \
freetype-devel \
gmp-devel \
libldb-devel \
libc-client libc-client-devel \
openldap openldap-devel \
oniguruma oniguruma-devel \
net-snmp-devel readline-devel unixODBC-devel \
uw-imap uw-imap-devel uw-imap-static uw-imap-utils \
libicu-devel \
enchant2 enchant2-devel \
gd gd-devel \
libsodium libsodium-devel \
libtidy libtidy-devel

You may not receive error when issuing ./configure, make && make install. Even when you manually build your PHP extension package later. 

2. At step 5 - before modifying php.ini - you may double-check whether the current PHP is reading which php.ini file by this command

php -ini | grep php.ini 
# My result. It is different from tutorial. 
Configuration File (php.ini) Path => /usr/local/lib
Loaded Configuration File => /usr/local/lib/php.ini

When I run the following command to start the php-fpm:
/usr/local/bin/php-fpm

I got the following error information:
Unable to globalize '/usr/local/NONE/etc/php-fpm.d/*.conf' (ret=2) from /usr/local/etc/php-fpm.conf at line 143.

To fix this error, do:
change the string "include=NONE/etc/php-fpm.d/*.conf" to "include=etc/php-fpm.d/*.conf" in the file "/usr/local/etc/php-fpm.conf" with text editor.

After that, I try to start the php-fpm again and got error information again:
Nothing matches the include pattern '/usr/local/etc/php-fpm.d/*.conf' from /usr/local/etc/php-fpm.conf at line 143.

To fix this error, do:
cp /usr/local/etc/php-fpm.d/www.conf.default /usr/local/etc/php-fpm.d/www.conf

cp php/php.ini-development        php/lib/php.ini
cp php/etc/php-fpm.conf.default       php/etc/php-fpm.conf
cp php/etc/php-fpm.d/www.conf.default     php/etc/php-fpm.d/www.conf

If you get "File not found" error then add "root ROOT_DIR_LOCATION" directive to PHP location block i.e. "location ~* \.php$ { }" , where ROOT_DIR_LOCATION is root directory like "/usr/share/nginx/html" .

at step 3, after command "sudo make install"
if there is problem with pear.php.net (https). Need to change this line (from https to http) in Makefile
PEAR_INSTALLER_URL = http://pear.php.net/install-pear-nozlib.phar

Great effort for this tutorial, thanks a ton, here are my notes if may help anyone, considering default install on WSL2 container
Note: composer added for Laravel framework.
These are NOT to be copy and pasted as it is, need to be selective as there are annotations beside some commands,
Also I've commented # some of the defaults written by the original editor due to mismatch to my current environment.

sha256sum  php-x.x.x.tar.gz => e847745fd66fc8c57fac993a609fefcded93fddccd225f0620a26bb5ae5753c3 
    tar zxf php-x.x.x
    sudo apt install build-essential
    sudo apt install -y composer nginx pkgconf libxml2-dev  libsqlite3-dev zlib1g-dev
    cd php-x.x.x
    ./configure --enable-fpm --with-mysqli <==Thank you for installing PHP.
        make <== takes a while 
    sudo make test <== optional as recommended
    sudo make install <= /usr/local/bin /usr/local/php
    sudo cp php.ini-development /usr/local/lib/php.ini
    sudo cp /usr/local/etc/php-fpm.d/www.conf.default /usr/local/etc/php-fpm.d/www.conf
    sudo cp sapi/fpm/php-fpm /usr/local/bin
    sudo vim /usr/local/php/php.ini <= cgi.fix_pathinfo=0
    sudo vim /usr/local/etc/php-fpm.d/www.conf <= user=www-data group=www-data
    sudo vim sapi/fpm/php-fpm.conf <= edit include=etc/php-fpm.d/*.conf  <- relative path
    sudo cp sapi/fpm/php-fpm.conf /usr/local/etc
    /usr/local/bin/php -v <= $PATH$ uses /usr/local/bin at first /usr/local/lib/php.ini
    sudo /usr/local/bin/php-fpm <= start the service
    sudo vim /etc/nginx/sites-available/default <= edit the following under server {}
    location / {
    #root   html;    
    #index  index.php index.html index.htm;
}
    location ~* \.php$ {
    #fastcgi_index   index.php;
    fastcgi_pass    127.0.0.1:9000;
    include         fastcgi_params;
    fastcgi_param   SCRIPT_FILENAME    $document_root$fastcgi_script_name;
    fastcgi_param   SCRIPT_NAME        $fastcgi_script_name;
}
    
    *Restart nginx (root /var/www/html) if root path doesn't exist, default is: /usr/share/nginx/html
    sudo nginx -t <= Test Nginx conf files
    sudo service nginx reload
    sudo service nginx stop
    sudo service nginx start <= [OK]
    
php-fpm needs to be in a service, or kill process manually ps -aux | grep php-fpm ; kill <pid>

in linux system, if you want to add php-fpm service to system service;  it is easy to do that, because php offer the relate shell script:

after make and make install;enter the source code package sapi/fpm/init.d.php-fpm ; type the code in the linux system.  
cp sapi/fpm/init.d.php-fpm  /etc/init.d/php-fpm

then you can use "php-fpm {start|stop|force-quit|restart|reload|status|configtest} "  command  to control your php-fpm program more convenient .