[MC][AsmParser] Hook for post assembly file processing

This patch handles LLVM standalone assembler (llvm-mc) ELF flag setting based on input file
directive processing.

Mips assembly requires processing inline directives that directly and
indirectly affect the output ELF header flags. This patch handles one
".abicalls".

To process these directives we are following the model the code generator
uses by storing state in a container as we go through processing and when
we detect the end of input file processing, AsmParser is notified and we
update the ELF header flags through a MipsELFStreamer method with a call from
MCTargetAsmParser::emitEndOfAsmFile(MCStreamer &OutStreamer).

This patch will allow other targets the same functionality.

Jack


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191982 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/MC/MCTargetAsmParser.h

@@ -176,6 +176,11 @@ public:
   virtual void convertToMapAndConstraints(unsigned Kind,
                       const SmallVectorImpl<MCParsedAsmOperand*> &Operands) = 0;
 
+  /// End of assembly processing.
+  /// This gets called when all assembly has been read and gives the local
+  /// Target AsmParsers an opportunity for any final data processing, etc..
+  virtual void emitEndOfAsmFile(MCStreamer &Out) {}
+
   virtual const MCExpr *applyModifierToExpr(const MCExpr *E,
                                             MCSymbolRefExpr::VariantKind,
                                             MCContext &Ctx) {