Force function-pointer CPU dispatch for zig builds to fix silent lld crash

Root cause of the intermittent 'Aborted (core dumped) zig-cc' at the
sapi/cli/php LTO link, proven by byte-exact local replay of the CI link
(lld --reproduce) and single-file bisection:

PHP's configure probes __builtin_cpu_supports/__builtin_cpu_init with a
link test that runs under -flto. Whether zig resolves compiler-rt's
__cpu_model in that probe varies by machine, so the result is a per-VM
lottery. When it says yes, zend_portability.h enables
ZEND_INTRIN_*_FUNC_PROTO and mbstring/standard compile
__attribute__((ifunc)) AVX2 resolvers. An ifunc in full-LTO bitcode
crashes zig 0.16's lld (LLVM 21.1.0): during LTO prevailing-symbol
resolution it dereferences a null summary for the local symbol
mb_cut_utf16le (GUID 0x151eb2c1758fcd09 = md5_64 of
'<mbfilter_utf16.c>;mb_cut_utf16le'), and the zig driver swallows the
child's SIGSEGV, leaving no output.

Verified both directions: compiling mbfilter_utf16.o with the cpu
builtins defined produces the ifunc object and the link crashes;
compiling with them off produces the function-pointer object and the
same link succeeds.

Forcing the configure cache vars to no (like the existing avx512
overrides) makes every build take the safe, deterministic
function-pointer dispatch path. Runtime cost is a pointer call instead
of an ifunc-resolved call for a handful of mb/crc32 functions.

Author: henderkes

config/templates/craft.yml.twig

@@ -97,7 +97,13 @@ extra-env:
     SPC_MUSL_DYNAMIC: 'true'
     {% else -%}
     SPC_TARGET: '{{ target }}'
-    SPC_EXTRA_PHP_VARS: 'php_cv_preserve_none=yes'
+    # __builtin_cpu_supports=yes makes PHP emit __attribute__((ifunc)) AVX2 resolvers
+    # (mbstring, standard), and ifuncs in full-LTO bitcode crash zig 0.16's lld
+    # (LLVM 21.1.0) with a silent SIGSEGV during LTO symbol resolution. The configure
+    # probe itself is an -flto link test whose result varies per machine (zig
+    # compiler_rt __cpu_model resolution), which made the crash look random per VM.
+    # Force the safe function-pointer dispatch path instead.
+    SPC_EXTRA_PHP_VARS: 'php_cv_preserve_none=yes php_cv_have___builtin_cpu_supports=no php_cv_have___builtin_cpu_init=no'
     # zig cc without -O keeps Debug UB traps; bare-built minilua aborts on Lua's 2^32 double->int cast
     SPC_COMPILER_EXTRA: '-fno-sanitize=undefined'
     {% endif -%}