Replace uses of _W64 with MINGW_W64

This is the `master' branch follow-up to the change made previously on
the emacs-24 branch (81e0cca7bb).

    * src/w32.c: Use MINGW_W64 instead of _W64.

    * src/w32heap.c: Likewise.

src/ChangeLog

@@ -1,3 +1,9 @@
+2014-11-27  Oscar Fuentes  <ofv@wanadoo.es>
+
+	* src/w32.c: Use MINGW_W64 instead of _W64.
+
+	* src/w32heap.c: Likewise.
+
 2014-11-17  Oscar Fuentes  <ofv@wanadoo.es>
 
 	* src/w32.c: Use MINGW_W64 instead of _W64.

src/w32.c

@@ -72,7 +72,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <pwd.h>
 #include <grp.h>
 
-/* MinGW64 (_W64) defines these in its _mingw.h.  */
+/* MinGW64 defines these in its _mingw.h.  */
 #ifndef _ANONYMOUS_UNION
 # define _ANONYMOUS_UNION
 #endif

src/w32heap.c

@@ -214,7 +214,7 @@ dumped_data_commit (PVOID Base, PVOID *CommitAddress, PSIZE_T CommitSize)
 
 /* We want to turn on Low Fragmentation Heap for XP and older systems.
    MinGW32 lacks those definitions.  */
-#ifndef _W64
+#ifndef MINGW_W64
 typedef enum _HEAP_INFORMATION_CLASS {
   HeapCompatibilityInformation
 } HEAP_INFORMATION_CLASS;
@@ -244,7 +244,7 @@ init_heap (void)
       /* Create the private heap.  */
       heap = HeapCreate (0, 0, 0);
 
-#ifndef _W64
+#ifndef MINGW_W64
       /* Set the low-fragmentation heap for OS before Vista.  */
       HMODULE hm_kernel32dll = LoadLibrary ("kernel32.dll");
       HeapSetInformation_Proc s_pfn_Heap_Set_Information = (HeapSetInformation_Proc) GetProcAddress (hm_kernel32dll, "HeapSetInformation");