[PATCH] MC: Add support for BigObj

[Reid Kleckner]

Looks fine to me. Up to you if you want to wait for Rui for a more object-file oriented review.

================
Comment at: lib/MC/WinCOFFObjectWriter.cpp:658
@@ -634,2 +657,3 @@
       Write8(i->Aux.SectionDefinition.Selection);
-      WriteZeros(sizeof(i->Aux.SectionDefinition.unused));
+      WriteZeros(1);
+      if (UseBigObj)
----------------
Write8(0) doesn't have a loop? *shrug*

================
Comment at: lib/MC/WinCOFFObjectWriter.cpp:662
@@ +661,3 @@
+      else
+        WriteZeros(2);
+      if (UseBigObj)
----------------
WriteLE16(0)?

http://reviews.llvm.org/D5349