[PATCH] MS ABI: Mangle null pointer-to-member-functions compatibly

[Reid Kleckner]

lgtm

Feel free to commit with a test for the null data memptr of a non-dynamic class.

================
Comment at: lib/AST/MicrosoftMangle.cpp:539
@@ +538,3 @@
+    if (IM == MSInheritanceAttr::Keyword_single_inheritance) {
+      Out << "$0A@";
+      return;
----------------
What happens if -1 is the null representation?  This happens for data memptrs of non-dynamic classes.

http://reviews.llvm.org/D4059