don't need to inline, simplify to always use FMT_CONSTEXPR if it's defined

include/spdlog/common.h

@@ -70,19 +70,13 @@
     #define SPDLOG_CONSTEXPR constexpr
 #endif
 
-// If building with std::format, can just use constexpr, otherwise if building with fmt
-// SPDLOG_CONSTEXPR_FUNC needs to be set the same as FMT_CONSTEXPR to avoid situations where
-// a constexpr function in spdlog could end up calling a non-constexpr function in fmt
-// depending on the compiler
-// If fmt determines it can't use constexpr, we should inline the function instead
-#ifdef SPDLOG_USE_STD_FORMAT
+// If building with fmt SPDLOG_CONSTEXPR_FUNC needs to be set the same as FMT_CONSTEXPR
+// to avoid situations where a constexpr function in spdlog could end up calling
+// a non-constexpr function in fmt depending on the compiler
+#ifdef FMT_CONSTEXPR
+    #define SPDLOG_CONSTEXPR_FUNC FMT_CONSTEXPR
+#else
     #define SPDLOG_CONSTEXPR_FUNC constexpr
-#else  // Being built with fmt
-    #if FMT_USE_CONSTEXPR
-        #define SPDLOG_CONSTEXPR_FUNC FMT_CONSTEXPR
-    #else
-	#define SPDLOG_CONSTEXPR_FUNC inline
-    #endif
 #endif
 
 #if defined(__GNUC__) || defined(__clang__)