Add support for C++ default arguments, and rework Parse-Sema 
interaction for function parameters, fixing PR2046.

Patch by Doug Gregor!

llvm-svn: 49369
diff --git a/clang/test/Sema/default1.c b/clang/test/Sema/default1.c
new file mode 100644
index 0000000..a72d0ae
--- /dev/null
+++ b/clang/test/Sema/default1.c
@@ -0,0 +1,2 @@
+// RUN: clang -fsyntax-only -verify %s
+void f(int i = 0); // expected-error {{C does not support default arguments}}