Add mimalloc support for macOS and Linux

[DubbleClick]

What does this PR do?

add mimalloc as an optional library.
if building with --with-libs="mimalloc", it replaces the libc allocator.

Fix #662

Checklist before merging

If your PR involves the changes mentioned below and completed the action, please tick the corresponding option.
If a modification is not involved, please skip it directly.

• If you modified *.php, run composer cs-fix at local machine.
• If it's an extension or dependency update, make sure adding related extensions in src/global/test-extensions.php.
• If you changed the behavior of static-php-cli, update docs in ./docs/.
• If you updated config/xxx.json content, run bin/spc dev:sort-config xxx.

[crazywhalecc]

Is it linux-only feature?

[DubbleClick]

no, this works on macos too.

on windows it would work too, but there's less benefit to it. fully static windows builds can still preload the shared mimalloc library if someone wants and msvc's default allocator is fast anyway.

[DubbleClick]

this will majorly simplify frankenphp's mimalloc build (can get rid of the whole patch code and only need to set buildroot/lib/mimalloc.o as the first "library" in CGO_LDFLAGS.

it's also nice for static-php-cli compiling cli/fpm because musl's allocator is awfully slow in threaded scenarios

[crazywhalecc]

Ready to merge?

[DubbleClick]

in theory yes, chinese docs are missing and some php 8.1 tests seem to fail

[DubbleClick]

never mind, chinese dovs are not missing :)

[DubbleClick]

Ready to merge?

yes ready to merge now