strsep is BSD|GNU, not GNU-only; it's originally from BSD

include/string.h

@@ -79,6 +79,10 @@ size_t strxfrm_l (char *__restrict, const char *__restrict, size_t, locale_t);
 void *memccpy (void *__restrict, const void *__restrict, int, size_t);
 #endif
 
+#if defined(_GNU_SOURCE) || defined(_BSD_SOURCE)
+char *strsep(char **, const char *);
+#endif
+
 #ifdef _BSD_SOURCE
 size_t strlcat (char *, const char *, size_t);
 size_t strlcpy (char *, const char *, size_t);
@@ -91,7 +95,6 @@ int strcasecmp_l (const char *, const char *, locale_t);
 int strncasecmp_l (const char *, const char *, size_t, locale_t);
 char *strchrnul(const char *, int);
 char *strcasestr(const char *, const char *);
-char *strsep(char **, const char *);
 void *memrchr(const void *, int, size_t);
 void *mempcpy(void *, const void *, size_t);
 #ifndef __cplusplus