[libc] Add *_HAS_SUBNORM to float.h (#102182)

Summary:
These should be defined, since we provide `float.h` it will override the
Clang resource dir and not provide it.

libc/include/llvm-libc-macros/float-macros.h

@@ -161,6 +161,18 @@
 #define LDBL_MAX_10_EXP __LDBL_MAX_10_EXP__
 #endif // LDBL_MAX_10_EXP
 
+#ifndef FLT_HAS_SUBNORM
+#define FLT_HAS_SUBNORM __FLT_HAS_DENORM__
+#endif // FLT_HAS_SUBNORM
+
+#ifndef DBL_HAS_SUBNORM
+#define DBL_HAS_SUBNORM __DBL_HAS_DENORM__
+#endif // DBL_HAS_SUBNORM
+
+#ifndef LDBL_HAS_SUBNORM
+#define LDBL_HAS_SUBNORM __LDBL_HAS_DENORM__
+#endif // LDBL_HAS_SUBNORM
+
 // TODO: Add FLT16 and FLT128 constants.
 
 #endif // LLVM_LIBC_MACROS_FLOAT_MACROS_H