Rebased PNaCl localmods in LLVM to 223109

lib/Support/MemoryBuffer.cpp

Index: lib/Support/MemoryBuffer.cpp
diff --git a/lib/Support/MemoryBuffer.cpp b/lib/Support/MemoryBuffer.cpp
index 7eb0752c22201d44d79fedcbb8f3fe4782d586aa..d6f7f545753bc2f4c3dfb39824890d590173e172 100644
--- a/lib/Support/MemoryBuffer.cpp
+++ b/lib/Support/MemoryBuffer.cpp
@@ -273,10 +273,21 @@ getFileAux(const Twine &Filename, int64_t FileSize, uint64_t MapSize,
 static bool shouldUseMmap(int FD,
                           size_t FileSize,
                           size_t MapSize,
-                          off_t Offset,
+                          int64_t Offset,   // @LOCALMOD (?)
                           bool RequiresNullTerminator,
                           int PageSize,
                           bool IsVolatileSize) {
+
+  // @LOCALMOD-BEGIN
+  // Post 3.3-merge there seems to be a problem using mmap on cygwin. In the
+  // meantime, as a LOCALMOD, we disable usage of mmap in MemoryBuffer. The
+  // effect of this on the Windows/Cygwin toolchain can be a slightly slower
+  // developer-side linkage time.
+#if defined(__CYGWIN__)
+  return false;
+#endif
+  // @LOCALMOD-END
+
   // mmap may leave the buffer without null terminator if the file size changed
   // by the time the last page is mapped in, so avoid it if the file size is
   // likely to change.