[gtk/isnanf-cleanup] fallback-c89: Try to make isnanf work

[Christoph Reiter <creiter src gnome org>]

commit c5829bd0e2134ed9f05fe9d6fbe1f3156a00352e
Author: Christoph Reiter <reiter christoph gmail com>
Date:   Sun May 31 15:09:31 2020 +0200

    fallback-c89: Try to make isnanf work

 gtk/fallback-c89.c | 26 +++++++++++---------------
 1 file changed, 11 insertions(+), 15 deletions(-)
---
diff --git a/gtk/fallback-c89.c b/gtk/fallback-c89.c
index 505d52e13a..65cb53589e 100644
--- a/gtk/fallback-c89.c
+++ b/gtk/fallback-c89.c
@@ -20,6 +20,7 @@
 #include "config.h"
 
 #include <math.h>
+#include <float.h>
 
 /* Workaround for round() for non-GCC/non-C99 compilers */
 #ifndef HAVE_ROUND
@@ -93,26 +94,21 @@ isnan (double x)
 #endif
 
 #ifndef HAVE_DECL_ISNANF
-#if 1
-#define isnanf(x) isnan(x)
-#else
-/* it seems of the supported compilers only
- * MSVC does not have isnanf(), but it does
- * have _isnanf() which does the same as isnanf()
- */
-#ifdef _MSC_VER
-static inline gboolean
-isnanf (float x)
-{
-  return _isnanf (x);
-}
-#elif defined (__GNUC__)
+#if defined (__GNUC__)
 /* gcc has an intern function that it warns about when
  * using -Wshadow but no header properly declares it,
  * so we do it instead.
  */
 extern int isnanf (float x);
-#endif
+#else
+static inline int
+isnanf (float x)
+{
+  /* Either use the C99 type infering macro, or the fallback from above.
+   * MSVC has _isnanf, but only on x64
+   */
+  return isnan (x);
+}
 #endif
 #endif