[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)

[Aaron Ballman 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>
----------------
AaronBallman wrote:

Previously, the macro was always defined, now it's only being defined for `__MVS__`, is that intentional?

I took a look on SourceGraph and it doesn't look like anyone is testing `__CLANG_FLOAT_H`, but it's possible someone is relying on that to determine whether float.h was included for Clang or not.

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