(strtoul): Do not declare if HAVE_DECL_STRTOUL.
(strtoimax, strtoumax): Do not declare if already defined as a macro.
#include "xstrtol.h"
-#ifndef strtol
+#if !HAVE_DECL_STRTOL && !defined strtol
long int strtol ();
#endif
-#ifndef strtoul
+#if !HAVE_DECL_STRTOUL && !defined strtoul
unsigned long int strtoul ();
#endif
-#if !HAVE_DECL_STRTOIMAX
+#if !HAVE_DECL_STRTOIMAX && !defined strtoimax
intmax_t strtoimax ();
#endif
-#if !HAVE_DECL_STRTOUMAX
+#if !HAVE_DECL_STRTOUMAX && !defined strtoumax
uintmax_t strtoumax ();
#endif