php8: fix cross-compiling for x86_64

php8: fix cross-compiling for x86_64

The build process uses a minilua helper for code generation
which must not be compiled with target cross-compiler but
the host compiler.

This error was spotted by buildbots:
ext/opcache/minilua /builder/shared-workdir/build/sdk/build_dir/
 target-x86_64_musl/php-8.0.1/ext/opcache/jit/dynasm/dynasm.lua
 -D X64=1 -o ext/opcache/jit/zend_jit_x86.c /builder/shared-workdir
 /build/sdk/build_dir/target-x86_64_musl/php-8.0.1/ext/opcache/jit/zend_jit_x86.dasc
/bin/bash: ext/opcache/minilua: No such file or directory
Makefile:406: recipe for target 'ext/opcache/jit/zend_jit_x86.c' failed
make[4]: *** [ext/opcache/jit/zend_jit_x86.c] Error 127

Signed-off-by: Michael Heimpold <mhei@heimpold.de>