Use __WIN64__ instead of MSVC-specific _WIN64 in wxIsPlatform64Bit().

Make the code work correctly for 64 bit builds with other compilers, e.g. gcc.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@76510 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/utils.cpp

@@ -1360,7 +1360,7 @@ wxString wxGetOsDescription()
 
 bool wxIsPlatform64Bit()
 {
-#if defined(_WIN64)
+#if defined(__WIN64__)
     return true;  // 64-bit programs run only on Win64
 #elif wxUSE_DYNLIB_CLASS // Win32
     // 32-bit programs run on both 32-bit and 64-bit Windows so check