Restore r125595 (reverted in r126336) with modifications:

Introduce a variable in the AsmParserExtension whether [] is valid in an
expression. If it is true, parse them like (). Enable this for ELF only.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@126443 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCParser/MCAsmParserExtension.h

@@ -38,6 +38,8 @@ protected:
     return (Obj->*Handler)(Directive, DirectiveLoc);
   }
 
+  bool BracketExpressionsSupported;
+
 public:
   virtual ~MCAsmParserExtension();
 
@@ -68,6 +70,8 @@ public:
 
   const AsmToken &getTok() { return getParser().getTok(); }
 
+  bool HasBracketExpressions() const { return BracketExpressionsSupported; }
+
   /// @}
 };