[PATCH] Fix .seh_stackalloc 0

[Reid Kleckner]

lgtm, I can commit this.

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Comment at: lib/MC/MCStreamer.cpp:518-519
@@ -517,2 +517,4 @@
   EnsureValidW64UnwindInfo();
+  if (Size == 0)
+    report_fatal_error("Allocation size must be non-zero!");
   if (Size & 7)
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MCStreamer needs a way to report errors....  :(

http://reviews.llvm.org/D4334