use regular fmt target if header-only does not exist

CMakeLists.txt

@@ -86,7 +86,8 @@ target_compile_options(
 target_link_libraries(
 	"${TARGET_NAME}"
 	PRIVATE
-		fmt::fmt-header-only
+		$<TARGET_NAME_IF_EXISTS:fmt::fmt-header-only>
+		$<$<NOT:$<TARGET_EXISTS:fmt::fmt-header-only>>:fmt::fmt>
 )
 
 # Copy binaries to project folder for debugging during development.