u8string doesn't make sense to test before char8_t

Author: Hana Dusíková

tests/_unicode.cpp

@@ -71,8 +71,10 @@ static_assert(CTRE_CREATE(U"\\p{script=Latin}+").match(U"abcd"));
 static_assert(CTRE_CREATE(U"\\p{script=Greek}+").match(U"βΩ"));
 static_assert(!CTRE_CREATE(U"\\p{script=Latin}+").match(U"βΩ"));
 static_assert(!CTRE_CREATE(U"\\p{script=Greek}+").match(U"abcd"));
+#if __cpp_char8_t >= 201811
 static_assert(CTRE_CREATE(U"\\p{emoji}+").match(u8"🤪😍"));
 static_assert(CTRE_CREATE("\\p{emoji}+").match(u8"🤪😍"));
+#endif
 static_assert(CTRE_CREATE(U"\\p{emoji}+").match(U"🤪😍✨\U0001F3F3"));
 static_assert(CTRE_SYNTAX(U"\\p{sc=greek}+?\\p{Emoji}\\p{sc=greek}+?"));
 static_assert(CTRE_CREATE(U"\\p{sc=greek}+?\\p{Emoji}").match(U"αΩ😍"));