Fix typo in FMT_HAS_BUILTIN check

Author: LocalSpook

include/fmt/base.h

@@ -537,7 +537,7 @@ template <typename Char> class basic_string_view {
   FMT_ALWAYS_INLINE
 #endif
   FMT_CONSTEXPR20 basic_string_view(const Char* s) : data_(s) {
-#if FMT_HAS_BUILTIN(__buitin_strlen) || FMT_GCC_VERSION || FMT_CLANG_VERSION
+#if FMT_HAS_BUILTIN(__builtin_strlen) || FMT_GCC_VERSION || FMT_CLANG_VERSION
     if (std::is_same<Char, char>::value) {
       size_ = __builtin_strlen(detail::narrow(s));
       return;