math: Do not use __builtin_isgreater* and __builtin_isless* on clang

math: Do not use __builtin_isgreater* and __builtin_isless* on clang

clang does not check for unordered numbers with builtins for 128-bit
float types (both _Float128 on x86_64 or long double on aarch64) [1].

For instance, the code:

  #ifdef __x86_64__
  typedef __float128 FLOAT128_TYPE;
  #elif defined (__aarch64__)
  typedef long double FLOAT128_TYPE;
  #endif

  int foo (FLOAT128_TYPE x, FLOAT128_TYPE y)
  {
    return __builtin_isgreater (x, y);
  }

Will issue a __gttf2 call instead of a __unordtf2 followed by the
comparison.

Using the generic implementation fixes multiple issues with math tests,
such as:

Failure: fmax (0, qNaN): Exception "Invalid operation" set
Failure: fmax (0, -qNaN): Exception "Invalid operation" set
Failure: fmax (-0, qNaN): Exception "Invalid operation" set
Failure: fmax (-0, -qNaN): Exception "Invalid operation" set
Failure: fmax (9, qNaN): Exception "Invalid operation" set
Failure: fmax (9, -qNaN): Exception "Invalid operation" set
Failure: fmax (-9, qNaN): Exception "Invalid operation" set
Failure: fmax (-9, -qNaN): Exception "Invalid operation" set

It has a small performance overhead due to the extra isunordered (which
could be omitted for float and double types). Using _Generic (similar to
how __MATH_TG) on a bivariadic function requires a lot of boilerplate
macros.

[1] https://github.com/llvm/llvm-project/issues/172499
Reviewed-by: H.J. Lu <hjl.tools@gmail.com>