Move FMT_MAYBE_UNUSED to format.h where it is used

include/fmt/core.h

@@ -159,14 +159,6 @@
 #  define FMT_NORETURN
 #endif
 
-#ifndef FMT_MAYBE_UNUSED
-#  if FMT_HAS_CPP17_ATTRIBUTE(maybe_unused)
-#    define FMT_MAYBE_UNUSED [[maybe_unused]]
-#  else
-#    define FMT_MAYBE_UNUSED
-#  endif
-#endif
-
 #if __cplusplus == 201103L || __cplusplus == 201402L
 #  if defined(__INTEL_COMPILER) || defined(__PGI)
 #    define FMT_FALLTHROUGH

include/fmt/format.h

@@ -128,6 +128,14 @@ FMT_END_NAMESPACE
 #  endif
 #endif
 
+#ifndef FMT_MAYBE_UNUSED
+#  if FMT_HAS_CPP17_ATTRIBUTE(maybe_unused)
+#    define FMT_MAYBE_UNUSED [[maybe_unused]]
+#  else
+#    define FMT_MAYBE_UNUSED
+#  endif
+#endif
+
 // Workaround broken [[deprecated]] in the Intel, PGI and NVCC compilers.
 #if FMT_ICC_VERSION || defined(__PGI) || FMT_NVCC
 #  define FMT_DEPRECATED_ALIAS