replace prototype for basename in string.h with non-prototype declaration

GNU programs may expect the GNU version of basename, which has a
different prototype (argument is const-qualified) and prototype it
themselves too. of course if they're expecting the GNU behavior for
the function, they'll still run into problems, but at least this
eliminates some compile-time failures.

include/string.h

@@ -85,7 +85,7 @@ 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);
-char *basename(char *);
+char *basename();
 #endif
 
 #ifdef __cplusplus