do not use gsl::byte if it is deprecated

include/gsl/byte

@@ -74,6 +74,12 @@
 #define byte_may_alias
 #endif // defined __clang__ || defined __GNUC__
 
+#if GSL_USE_STD_BYTE
+#define BYTE_TYPE std::byte
+#else // !GSL_USE_STD_BYTE
+#define BYTE_TYPE byte
+#endif // GSL_USE_STD_BYTE
+
 #if GSL_USE_STD_BYTE
 #include <cstddef>
 #endif
@@ -158,10 +164,11 @@ constexpr IntegerType to_integer(byte b) noexcept
 
 #endif // GSL_USE_STD_BYTE
 
+
 template <typename T>
 // NOTE: need suppression since c++14 does not allow "return {t}"
 // GSL_SUPPRESS(type.4) // NO-FORMAT: attribute // TODO: suppression does not work
-constexpr byte to_byte(T t) noexcept
+constexpr BYTE_TYPE to_byte(T t) noexcept
 {
     static_assert(std::is_same<T, unsigned char>::value,
                   "gsl::to_byte(t) must be provided an unsigned char, otherwise data loss may occur. "
@@ -170,7 +177,7 @@ constexpr byte to_byte(T t) noexcept
 }
 
 template <int I>
-constexpr byte to_byte() noexcept
+constexpr BYTE_TYPE to_byte() noexcept
 {
     static_assert(I >= 0 && I <= 255,
                   "gsl::byte only has 8 bits of storage, values must be in range 0-255");