[mips] [IAS] Implement the .asciiz directive.

Summary:
This directive is exactly the same as .asciz, except it's only used by MIPS.
It is used to store null terminated strings in object files.

Reviewers: rafael, dsanders, echristo

Reviewed By: dsanders, echristo

Subscribers: echristo, llvm-commits

Differential Revision: http://reviews.llvm.org/D7530

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@235382 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCParser/AsmParser.cpp

@@ -184,6 +184,10 @@ public:
     ExtensionDirectiveMap[Directive] = Handler;
   }
 
+  void addAliasForDirective(StringRef Directive, StringRef Alias) override {
+    DirectiveKindMap[Directive] = DirectiveKindMap[Alias];
+  }
+
 public:
   /// @name MCAsmParser Interface
   /// {