[clang-tidy] Make test work on architectures which do not provide a __int128_t

See f10cee91ae. The test did still not run successful since the
`CHECK-MESSAGE` line is still read and considered even though the `#ifdef` removes the code if
`__int128_t` is not available. Now there is a fallback type in this case.

clang-tools-extra/test/clang-tidy/checkers/bugprone-sizeof-expression.cpp

@@ -288,10 +288,12 @@ int Test6() {
 
 #ifdef __SIZEOF_INT128__
 template <__int128_t N> 
+#else
+template <long N> // Fallback for platforms which do not define `__int128_t`
+#endif
 bool Baz() { return sizeof(A) < N; }
 // CHECK-MESSAGES: :[[@LINE-1]]:21: warning: suspicious comparison of 'sizeof(expr)' to a constant
 bool Test7() { return Baz<-1>(); }
-#endif
 
 int ValidExpressions() {
   int A[] = {1, 2, 3, 4};