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
diff --git a/llvm/lib/Support/Windows/Path.inc b/llvm/lib/Support/Windows/Path.inc
index f65ed5c..dd42055 100644
--- a/llvm/lib/Support/Windows/Path.inc
+++ b/llvm/lib/Support/Windows/Path.inc
@@ -734,8 +734,8 @@
 
   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());