Fixe bogus error for variable argument methods. Sema::ObjcGetTypeForMethodDefinition() wasn't preserving the isVariadic boolean. Another fix is to avoid synthsizing the function decl entirely, however this is a separate issue that I don't want to deal with now. Also added a FIXME to Sema::CheckFunctionCall(), which is currently emitting a bogus warning.

llvm-svn: 45146