Description:
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It may be a documentation or build problem, not sure which exactly -- my limited testing suggests that build process mistakenly disables JIT.

https://wiki.php.net/rfc/jit states "Currently we support x86 and x86_64 on POSIX platforms" -- I get "x86" here means 32-bit x86.

I have a 32-bit system I've built PHP 8 on (8.0.3 and 8.0.5). JIT was "unavailable" in phpinfo(), and I've found "WARNING: JIT not supported by host architecture" in config.log.

Checking "configure", I've found, that the test for said architecture is:

    case $host_cpu in
      x86*)
        ;;
      *)
        { $as_echo "$as_me:${as_lineno-$LINENO}: WARNING: JIT not supported by host architecture" >&5
$as_echo "$as_me: WARNING: JIT not supported by host architecture" >&2;}
        PHP_OPCACHE_JIT=no
        ;;
    esac

BUT $host_cpu on my system is recognized as "i686", so the "x86*" condition never matches.

Out of curiosity, I've modified the condition to match my CPU and rebuilt PHP; now phpinfo() reports JIT as "On", opcache_get_status() says it's "enabled" and "on", and so far I haven't encountered a single problem running various scripts (I haven't measured performance yet, though). So -- is there a mistake in docs, and for some reason JIT really should not be used on 32bit systems, or a mistake in configure script?