Fix completely bogus types for some builtins:

 * In C++, never create a FunctionNoProtoType for a builtin (fixes C++1z
   crasher from r289754).

 * Fix type of __sync_synchronize to be a no-parameter function rather than a
   varargs function. This matches GCC.

 * Fix type of vfprintf to match its actual type. We gave it a wrong type due
   to PR4290 (apparently autoconf generates invalid code and expects compilers
   to choke it down or it miscompiles the program; the relevant error in clang
   was downgraded to a warning in r122744 to fix other occurrences of this
   autoconf brokenness, so we don't need this workaround any more).

 * Turn off vararg argument checking for __noop, since it's not *really* a
   varargs function. Alternatively we could add custom type checking for it
   and synthesize parameter types matching the actual arguments in each call,
   but that seemed like overkill.

llvm-svn: 290146
diff --git a/clang/lib/AST/ASTContext.cpp b/clang/lib/AST/ASTContext.cpp
index 0ad663f..4abca4c 100644
--- a/clang/lib/AST/ASTContext.cpp
+++ b/clang/lib/AST/ASTContext.cpp
@@ -8729,8 +8729,8 @@
 
   bool Variadic = (TypeStr[0] == '.');
 
-  // We really shouldn't be making a no-proto type here, especially in C++.
-  if (ArgTypes.empty() && Variadic)
+  // We really shouldn't be making a no-proto type here.
+  if (ArgTypes.empty() && Variadic && !getLangOpts().CPlusPlus)
     return getFunctionNoProtoType(ResType, EI);
 
   FunctionProtoType::ExtProtoInfo EPI;