numeric.c: no declaration of finite

* numeric.c (finite): disable declaration on Windows, which can be
  defined in ruby/win32.h.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43235 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

numeric.c

@@ -30,7 +30,7 @@
 #include <ieeefp.h>
 #endif
 
-#if defined HAVE_FINITE && !defined finite
+#if defined HAVE_FINITE && !defined finite && !defined _WIN32
 extern int finite(double);
 #endif