Update macro names

Make global logic easier.

example/exm-lib.c

@@ -1,5 +1,5 @@
 // Request M*LIB to define functions
 // This include both m-string functions and array_str templated functions
 // Defining M_USE_EXTERN_DEF override M_USE_EXTERN_DECL definition
-#define M_USE_EXTERN_DEF
+#define M_USE_DEF
 #include "exm-header.h"