* missing/isnan.c (isnan): Don't define if isnan() macro is defined.

This fixes a compilation failure on uClibc based Gentoo system.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40422 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

missing/isnan.c

@@ -2,6 +2,20 @@
 
 #include "ruby/missing.h"
 
+/*
+ * isnan() may be a macro, a function or both.
+ * (The C99 standard defines that isnan() is a macro, though.)
+ * http://www.gnu.org/software/automake/manual/autoconf/Function-Portability.html
+ *
+ * macro only: uClibc
+ * both: GNU libc
+ *
+ * This file is compile if no isnan() function is available.
+ * (autoconf AC_REPLACE_FUNCS detects only the function.)
+ * The macro is detected by following #ifndef.
+ */
+
+#ifndef isnan
 static int double_ne(double n1, double n2);
 
 int
@@ -15,3 +29,4 @@ double_ne(double n1, double n2)
 {
     return n1 != n2;
 }
+#endif