Add missing test for warning added in r310803.

llvm-svn: 310978

clang/test/Lexer/cxx2a_keyword_as_cxx17.cpp

@@ -0,0 +1,9 @@
+// RUN: %clang_cc1 %s -verify -fsyntax-only -Wc++2a-compat -std=c++17
+
+#define concept constexpr bool
+template<typename T>
+concept x = 0;
+#undef concept
+
+int concept = 0; // expected-warning {{'concept' is a keyword in C++2a}}
+int requires = 0; // expected-warning {{'requires' is a keyword in C++2a}}