Fix parsing of .symver directive on ARM

ARM assembly syntax uses @ for a comment, execpt for the second
parameter of the .symver directive which requires @ as part of the
symbol name. This commit fixes the parsing of this directive by
adding a special case for ARM for this one argumnet.

To make the change we had to move the AllowAtInIdentifier variable
to the MCAsmLexer interface (from AsmLexer) and expose a setter for
the value.  The ELFAsmParser then toggles this value when parsing
the second argument to the .symver directive for a target that
uses @ as a comment symbol


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199339 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCParser/MCAsmLexer.h

@@ -118,6 +118,7 @@ class MCAsmLexer {
 protected: // Can only create subclasses.
   const char *TokStart;
   bool SkipSpace;
+  bool AllowAtInIdentifier;
 
   MCAsmLexer();
 
@@ -170,6 +171,9 @@ public:
 
   /// setSkipSpace - Set whether spaces should be ignored by the lexer
   void setSkipSpace(bool val) { SkipSpace = val; }
+
+  bool getAllowAtInIdentifier() { return AllowAtInIdentifier; }
+  void setAllowAtInIdentifier(bool v) { AllowAtInIdentifier = v; }
 };
 
 } // End llvm namespace