[C23] Correct the type for INFINITY and NAN in freestanding

This amends bcb7c38 to correct the
type use for the two macros to be float rather than double. Also adds
additional test coverage.

#98018 was filed to track
the duplicate diagnostic issue that was discovered.

Author: AaronBallman

clang/lib/Headers/float.h

@@ -164,8 +164,8 @@
 #if (defined(__STDC_VERSION__) && __STDC_VERSION__ >= 202311L) ||              \
     !defined(__STRICT_ANSI__)
    /* C23 5.2.5.3.3p29-30 */
-#  define INFINITY (__builtin_inf())
-#  define NAN (__builtin_nan(""))
+#  define INFINITY (__builtin_inff())
+#  define NAN (__builtin_nanf(""))
 #endif
 
 #ifdef __STDC_WANT_IEC_60559_TYPES_EXT__

clang/test/Headers/float.c

@@ -2,11 +2,14 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c99 -ffreestanding %s
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c11 -ffreestanding %s
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c23 -ffreestanding %s
-// RUN: %clang_cc1 -fsyntax-only -verify -std=c23 -ffreestanding -ffinite-math-only %s
+// RUN: %clang_cc1 -fsyntax-only -verify=finite -std=c23 -ffreestanding -ffinite-math-only %s
 // RUN: %clang_cc1 -fsyntax-only -verify -xc++ -std=c++11 -ffreestanding %s
 // RUN: %clang_cc1 -fsyntax-only -verify -xc++ -std=c++14 -ffreestanding %s
 // RUN: %clang_cc1 -fsyntax-only -verify -xc++ -std=c++17 -ffreestanding %s
 // RUN: %clang_cc1 -fsyntax-only -verify -xc++ -std=c++23 -ffreestanding %s
+// NOTE: C++23 wasn't based on top of C23, so it gets no diagnostics for
+//       finite-math-only mode as happens in C. When C++ rebased onto C23, that
+//       is when we'll issue diagnostics for INFINITY and NAN use.
 // RUN: %clang_cc1 -fsyntax-only -verify -xc++ -std=c++23 -ffreestanding -ffinite-math-only %s
 // expected-no-diagnostics
 
@@ -218,6 +221,10 @@
   #ifndef NAN
     #error "Mandatory macro NAN is missing."
   #endif
+  // FIXME: the NAN diagnostic should only be issued once, not twice.
+  _Static_assert(_Generic(INFINITY, float : 1, default : 0), ""); // finite-warning {{use of infinity via a macro is undefined behavior due to the currently enabled floating-point options}}
+  _Static_assert(_Generic(NAN, float : 1, default : 0), ""); // finite-warning {{use of NaN is undefined behavior due to the currently enabled floating-point options}} \
+                                                                finite-warning {{use of NaN via a macro is undefined behavior due to the currently enabled floating-point options}}
 #else
   #ifdef INFINITY
     #error "Macro INFINITY should not be defined."