[test] Add crash test for Clang function type mismatch.

Author: varungandhi-apple

test/Sema/clang_fn_type_mismatch.swift

@@ -0,0 +1,5 @@
+// RUN: not --crash %target-typecheck-verify-swift -sdk %clang-importer-sdk -experimental-print-full-convention -use-clang-function-types
+
+import ctypes
+
+let _error : (@convention(c, cType: "(void *) (*)(void *)") (Int) -> Int)? = getFunctionPointer_()