[clang] [clang-tools-extra] [llvm] [clang][headers] Need a way for math.h to share the definitions of INIFINITY and NAN with float.h (PR #164348)

[Ian Anderson via cfe-commits]

================
@@ -7,13 +7,21 @@
  *===-----------------------------------------------------------------------===
  */
 
-#ifndef __CLANG_FLOAT_H
-#define __CLANG_FLOAT_H
-
 #if defined(__MVS__) && __has_include_next(<float.h>)
+#include <__float_header_macro.h>
 #include_next <float.h>
 #else
 
+#if !defined(__need_infinity_nan)
----------------
ian-twilightcoder wrote:

I didn't want to expose `__need_float_float` as something that clients could set. The pattern in the other builtins is to chop up all of their pieces and not just a few, which I think in this case would be each subsection of ISO/IEC 9899:2024 5.2, but that seemed a bit overkill.

https://github.com/llvm/llvm-project/pull/164348