meta/pp: fix preprocessor UB in tests

Usually I would've amended the previous commit, but it's useful to keep
it separate in this case as it makes easier to deal with this problem in
the future. Previously I didn't use a macro, instead I used
static_assert directly. However, using #if inside a function-like macro
invocation is UB for no good reason and Visual C++'s preprocessor
refuses to work correctly.

warning: C5101: use of preprocessor directive in function-like macro argument list is undefined behavior

meta/tests/pp/foldr.c++

@@ -11,14 +11,17 @@ ASSERT_EQUAL(
 	(AW_FOLD_RIGHT(AW_IDENTITY, AW_TO_STR, a, b, c)),
 	("a", "b", "c"));
 
+#if AW_COMPILER == AW_COMPILER_GCC
 ASSERT_EQUAL(
 	(AW_FOLD_RIGHT(AW_SEP_SEMI, AW_SEP_SPACE AW_DEFER, (int,a), (float,b), (char,c) );),
-#if AW_COMPILER == AW_COMPILER_GCC
 	(int a ; float b ; char c ;)
+);
 #else
+ASSERT_EQUAL(
+	(AW_FOLD_RIGHT(AW_SEP_SEMI, AW_SEP_SPACE AW_DEFER, (int,a), (float,b), (char,c) );),
 	(int a; float b; char c;)
-#endif
 );
+#endif
 
 ASSERT_EQUAL(
 	(AW_FOREACH(AW_TO_STR, a, b, c)),

meta/tests/pp/struct.c++

@@ -6,52 +6,61 @@
 
 // TODO: strip spaces to eliminate differences in the preprocessor behaviour
 
+#if AW_COMPILER == AW_COMPILER_GCC
 ASSERT_EQUAL(
 	(AW_LIST_MEMBER_TYPES(NAME, AW_TUPLE(int, x), AW_TUPLE(int, y))),
-#if AW_COMPILER == AW_COMPILER_GCC
 	(int , int)
+);
 #else
+ASSERT_EQUAL(
+	(AW_LIST_MEMBER_TYPES(NAME, AW_TUPLE(int, x), AW_TUPLE(int, y))),
 	(int, int)
-#endif
 );
+#endif
 
+#if AW_COMPILER == AW_COMPILER_GCC
 ASSERT_EQUAL(
 	(AW_DEFINE_STRUCT(s, AW_TUPLE(int, x), AW_TUPLE(int, y))),
-#if AW_COMPILER == AW_COMPILER_GCC
 	(struct s {
 		::aw::type_t<int> x ;
 		::aw::type_t<int> y ;
 		using tuple_type = std::tuple<int , int >;
 		constexpr operator tuple_type() { return { x , y }; }
 	})
+);
 #else
+ASSERT_EQUAL(
+	(AW_DEFINE_STRUCT(s, AW_TUPLE(int, x), AW_TUPLE(int, y))),
 	(struct s {
 		::aw::type_t<int> x;
 		::aw::type_t<int> y;
 		using tuple_type = std::tuple<int, int>;
 		constexpr operator tuple_type() { return { x, y }; }
 	})
-#endif
 );
+#endif
 
+#if AW_COMPILER == AW_COMPILER_GCC
 ASSERT_EQUAL(
 	(AW_DEFINE_STRUCT( str, (int, x), (int, y) )),
-#if AW_COMPILER == AW_COMPILER_GCC
 	(struct str {
 		::aw::type_t<int> x ;
 		::aw::type_t<int> y ;
 		using tuple_type = std::tuple<int , int >;
 		constexpr operator tuple_type() { return { x , y }; }
 	})
+);
 #else
+ASSERT_EQUAL(
+	(AW_DEFINE_STRUCT( str, (int, x), (int, y) )),
 	(struct str {
 		::aw::type_t<int> x;
 		::aw::type_t<int> y;
 		using tuple_type = std::tuple<int, int>;
 		constexpr operator tuple_type() { return { x, y }; }
 	})
-#endif
 );
+#endif
 
 AW_DEFINE_STRUCT(s, AW_TUPLE(int, x), AW_TUPLE(int, y));