Fix some undefined beahvior in FileMapping.

This was broken when building a 32-bit native toolchain, as
shifting a size_t right by 32 is UB when sizeof(size_t) == 8.

llvm-svn: 318462

llvm/lib/Support/Windows/Path.inc

@@ -734,8 +734,8 @@ std::error_code mapped_file_region::init(int FD, uint64_t Offset,
 
   HANDLE FileMappingHandle =
       ::CreateFileMappingW(FileHandle, 0, flprotect,
-                           Size >> 32,
-                           Size & 0xffffffff,
+                           Hi_32(Size),
+                           Lo_32(Size),
                            0);
   if (FileMappingHandle == NULL) {
     std::error_code ec = mapWindowsError(GetLastError());