Make ParmVarDecl::getDefaultArg() more robust, it now asserts that the argument is not unparsed. Add a new hasDefaultArg() and use it in places where getDefaultArg() was called when the argument was unparsed.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@72984 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index cb3ec1f..dfec106 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -489,7 +489,7 @@
 unsigned FunctionDecl::getMinRequiredArguments() const {
   unsigned NumRequiredArgs = getNumParams();
   while (NumRequiredArgs > 0
-         && getParamDecl(NumRequiredArgs-1)->getDefaultArg())
+         && getParamDecl(NumRequiredArgs-1)->hasDefaultArg())
     --NumRequiredArgs;
 
   return NumRequiredArgs;