Eliminate warning from '_' being redefined in sepdebugcrcfix.c

Exposed by commit cf6c87997f which
includes system.h which includes the NLS stuff.

tools/sepdebugcrcfix.c

@@ -33,7 +33,9 @@
 #include <libelf.h>
 #include <gelf.h>
 
+#ifndef _
 #define _(x) x
+#endif
 #define static_assert(expr) \
   extern int never_defined_just_used_for_checking[(expr) ? 1 : -1]
 #ifndef min