fix for overly sensitive gcc

Author: hanickadot

tests/generating.cpp

@@ -53,7 +53,8 @@ static_assert(same_f(CTRE_GEN("(?:abc)"), ctre::string<'a','b','c'>()));
 static_assert(same_f(CTRE_GEN("\\x40"), ctre::character<char{0x40}>()));
 static_assert(same_f(CTRE_GEN("\\x7F"), ctre::character<char{0x7F}>()));
 // only characters with value < 128 are char otherwise they are internally char32_t
-constexpr bool char_is_unsigned = (std::numeric_limits<char>::max)() == 255;
+constexpr unsigned char_length = (std::numeric_limits<char>::max)();
+constexpr bool char_is_unsigned = (char_length == 255);
 // I wish I could have operator implication here :(
 using expected_type = std::conditional_t<char_is_unsigned, char, char32_t>;
 static_assert(same_f(CTRE_GEN("\\x80"), ctre::character<expected_type{0x80}>()));