[clang][Interp] Add missing static_assert message

This broke builders, e.g:
https://lab.llvm.org/buildbot/#builders/139/builds/38457

diff --git a/clang/test/AST/Interp/functions.cpp b/clang/test/AST/Interp/functions.cpp
index 4b81e7d..06edcde 100644 (file)
--- a/clang/test/AST/Interp/functions.cpp
+++ b/clang/test/AST/Interp/functions.cpp
@@ -10,7 +10,7 @@ static_assert(gimme5() == 5, "");
 
 
 template<typename T> constexpr T identity(T t) {
-  static_assert(true);
+  static_assert(true, "");
   return t;
 }
 static_assert(identity(true), "");