Add test coverage for invalid conversion functions with default args.

This currently leaks memory (PR19689) but wasn't covered by tests, so LSan
couldn't find it.

llvm-svn: 208477
diff --git a/clang/test/SemaCXX/conversion-function.cpp b/clang/test/SemaCXX/conversion-function.cpp
index 1d5700d..dcc0609 100644
--- a/clang/test/SemaCXX/conversion-function.cpp
+++ b/clang/test/SemaCXX/conversion-function.cpp
@@ -26,6 +26,9 @@
 public:
   void operator bool(int, ...) const; // expected-error{{conversion function cannot have a return type}} \
   // expected-error{{conversion function cannot have any parameters}}
+
+  operator bool(int a = 4) const; // expected-error{{conversion function cannot have any parameters}}
+  
   
   operator float(...) const;  // expected-error{{conversion function cannot be variadic}}