add c2y

Author: 5chmidti

clang/include/clang/Testing/TestLanguage.def

@@ -31,6 +31,7 @@ TESTLANGUAGE_C(C, 99, c99, 1)
 TESTLANGUAGE_C(C, 11, c11, 2)
 TESTLANGUAGE_C(C, 17, c17, 3)
 TESTLANGUAGE_C(C, 23, c23, 4)
+TESTLANGUAGE_C(C, 26, c2y, 5)
 
 // TESTLANGUAGE_CXX(CXX, 98, c++98, 0)
 TESTLANGUAGE_CXX(CXX, 03, c++03, 1)