gc.c: malloc_usable_size

* gc.c (malloc_usable_size): use _msize() on Windows.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43762 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

configure.in

@@ -1009,6 +1009,7 @@ main()
 		ac_cv_type_struct_timeval=yes
                 ac_cv_func_clock_gettime=yes
                 ac_cv_func_clock_getres=yes
+		ac_cv_func_malloc_usable_size=no
 		AC_CHECK_TYPE([NET_LUID], [], [],
 			      [@%:@include <windows.h>
 		  	      @%:@include <iphlpapi.h>])

gc.c

@@ -35,6 +35,12 @@
 # define __has_feature(x) 0
 #endif
 
+#ifndef HAVE_MALLOC_USABLE_SIZE
+# ifdef _WIN32
+#   define malloc_usable_size(a) _msize(a)
+# endif
+#endif
+
 #if /* is ASAN enabled? */ \
     __has_feature(address_sanitizer) /* Clang */ || \
     defined(__SANITIZE_ADDRESS__)  /* GCC 4.8.x */