tools/ceph-dencoder/sstring.h: use char8_t instead of unsigned char

This fixes a build failure with libc++ (clang/LLVM).  This build
failure is correct: there exists no specialization for
`std::char_traits<unsigned char>`.  The standards-compliant way to use
unsigned chars in strings is to use `char8_t`.

Signed-off-by: Max Kellermann <[email protected]>

Author: MaxKellermann

src/common/sstring.hh

@@ -44,6 +44,7 @@ template <typename char_type, typename Size, Size max_size>
 class basic_sstring {
     static_assert(
             (std::is_same<char_type, char>::value
+             || std::is_same<char_type, char8_t>::value
              || std::is_same<char_type, signed char>::value
              || std::is_same<char_type, unsigned char>::value),
             "basic_sstring only supports single byte char types");

src/tools/ceph-dencoder/sstring.h

@@ -7,7 +7,7 @@
 class sstring_wrapper {
   using sstring16 = basic_sstring<char, uint32_t, 16>;
   sstring16 s1;
-  using sstring24 = basic_sstring<unsigned char, uint16_t, 24>;
+  using sstring24 = basic_sstring<char8_t, uint16_t, 24>;
   sstring24 s2;
  public:
   sstring_wrapper() = default;