[gtk/gtk-3-24] gtkcssshadowvalue.c: Fix build on older Visual Studio

[Chun-wei Fan <fanchunwei src gnome org>]

commit 6f54881851a2ac1e6fefb790d63d022ec5288ae9
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Thu Jul 16 18:28:06 2020 +0800

    gtkcssshadowvalue.c: Fix build on older Visual Studio
    
    This code made use of isnan(), which is not provided by pre-2013 Visual
    Studio, so fix the build by including fallback-c89.c in place of math.h,
    and update fallback-c89.c to include the implementation of isnan() for
    Visual Studio, which is copied from the fallback-c89.c in gdk/.

 gtk/fallback-c89.c      | 12 ++++++++++++
 gtk/gtkcssshadowvalue.c |  2 +-
 2 files changed, 13 insertions(+), 1 deletion(-)
---
diff --git a/gtk/fallback-c89.c b/gtk/fallback-c89.c
index 3fb24ad8b0..737983c049 100644
--- a/gtk/fallback-c89.c
+++ b/gtk/fallback-c89.c
@@ -114,3 +114,15 @@ trunc (double x)
   return (x > 0 ? floor (x) : ceil (x));
 }
 #endif
+
+#ifndef HAVE_DECL_ISNAN
+/* it seems of the supported compilers only
+ * MSVC does not have isnan(), but it does
+ * have _isnan() which does the same as isnan()
+ */
+static inline gboolean
+isnan (double x)
+{
+  return _isnan (x);
+}
+#endif
diff --git a/gtk/gtkcssshadowvalue.c b/gtk/gtkcssshadowvalue.c
index 074ef2b909..864bdef4b4 100644
--- a/gtk/gtkcssshadowvalue.c
+++ b/gtk/gtkcssshadowvalue.c
@@ -29,7 +29,7 @@
 #include "gtkrenderprivate.h"
 #include "gtkpango.h"
 
-#include <math.h>
+#include "fallback-c89.c"
 #include <float.h>
 
 #define CORNER_MASK_CACHE_MAX_SIZE 2000U