llvm-mc: Clean up some handling of symbol/section association to be more correct
(external was really undefined and there wasn't an explicit representation for
absolute symbols).
 - This still needs some cleanup to how the absolute "pseudo" section is dealt
   with, but I haven't figured out the nicest approach yet.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@79733 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCSymbol.cpp b/lib/MC/MCSymbol.cpp
index d032017..3c9894b 100644
--- a/lib/MC/MCSymbol.cpp
+++ b/lib/MC/MCSymbol.cpp
@@ -12,6 +12,10 @@
 
 using namespace llvm;
 
+// Sentinel value for the absolute pseudo section.
+const MCSection *MCSymbol::AbsolutePseudoSection =
+  reinterpret_cast<const MCSection *>(1);
+
 /// NeedsQuoting - Return true if the string \arg Str needs quoting, i.e., it
 /// does not match [a-zA-Z_.][a-zA-Z0-9_.]*.
 //