[NFC] Refactor the Preprocessor function that handles Macro definitions and rename Arguments to Parameters in Macro Definitions. 
  - Extracted the reading of the tokens out into a separate function.
  - Replace 'Argument' with 'Parameter' when referring to the identifiers of the macro definition (as opposed to the supplied arguments - MacroArgs - during the macro invocation).

This is in preparation for submitting patches for review to implement __VA_OPT__ which will otherwise just keep lengthening the HandleDefineDirective function and making it less comprehensible.

I will also directly update some extra clang tooling that is broken by the change from Argument to Parameter.

Hopefully the bots will stay appeased.

Thanks!

llvm-svn: 308190
diff --git a/clang/lib/Sema/SemaCodeComplete.cpp b/clang/lib/Sema/SemaCodeComplete.cpp
index 83c3bd2..3a53f25 100644
--- a/clang/lib/Sema/SemaCodeComplete.cpp
+++ b/clang/lib/Sema/SemaCodeComplete.cpp
@@ -2738,7 +2738,7 @@
     
     // Format a function-like macro with placeholders for the arguments.
     Result.AddChunk(CodeCompletionString::CK_LeftParen);
-    MacroInfo::arg_iterator A = MI->arg_begin(), AEnd = MI->arg_end();
+    MacroInfo::param_iterator A = MI->param_begin(), AEnd = MI->param_end();
     
     // C99 variadic macros add __VA_ARGS__ at the end. Skip it.
     if (MI->isC99Varargs()) {
@@ -2749,8 +2749,8 @@
       }
     }
     
-    for (MacroInfo::arg_iterator A = MI->arg_begin(); A != AEnd; ++A) {
-      if (A != MI->arg_begin())
+    for (MacroInfo::param_iterator A = MI->param_begin(); A != AEnd; ++A) {
+      if (A != MI->param_begin())
         Result.AddChunk(CodeCompletionString::CK_Comma);
 
       if (MI->isVariadic() && (A+1) == AEnd) {