MC: Diagnose an unexpected token in COFF .section instead of asserting

This can easily arise when trying to assemble and ELF style .section
directive for a COFF object file.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215373 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCParser/COFFAsmParser.cpp

@@ -364,6 +364,10 @@ bool COFFAsmParser::ParseDirectiveSection(StringRef, SMLoc) {
 
     Flags |= COFF::IMAGE_SCN_LNK_COMDAT;
 
+    if (!getLexer().is(AsmToken::Identifier))
+      return TokError("expected comdat type such as 'discard' or 'largest' "
+                      "after protection bits");
+
     if (parseCOMDATType(Type))
       return true;