procio: remove glibc dependency & make a proper header

Duplicate that <libio.h> change made in master branch.

While we're at it, let's remove an unnecessary include
from procio.h and reflect in its single prototype what
those 'const char *' params are really supposed to be.

Signed-off-by: Jim Warner <james.warner@comcast.net>

lib/procio.c

@@ -24,7 +24,6 @@
 #endif
 #include <errno.h>
 #include <fcntl.h>
-#include <libio.h>
 #include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>