Fix compilation errors up until Clang 21.0

[kocsismate]

• The "pclmul" and "cldemote" CPU features are both only available on x86, and the __builtin_cpu_supports() checks in question fail on Clang, so they shouldn't even be tried to be run (similar fixes before: Fix build on Apple Clang 17+ #18629).
• The res.h file in Lexbor contains some unterminated strings (e.g.

  php-src/ext/lexbor/lexbor/html/tokenizer/res.h

  Line 203 in d58d3d2

  {0x76, {0}, 0, 367, 0, 368}, {0x3b, "\xe2\x89\xaa\xe2\x83\x92", 6, 0, 0, 0},

  ), and a new compiler warning fails by default because of them. This needs to be suppressed.

[ndossche]

Changes in Zend header are fine.
Compile fails because the warning flag you added for Lexbor may be unknown by the compiler.

[kocsismate]

@ndossche I had to push a small fix for 32-bit after your review. Could you please recheck it?