stdioext: Add tentative support for Plan9. * lib/stdio-impl.h: Include <errno.h>. * lib/fseterr.c (fseterr) [EPLAN9]: Add conditional code. * lib/freadable.c (freadable): Likewise. * lib/fwritable.c (fwritable): Likewise. * lib/fbufmode.c (fbufmode): Likewise. * lib/freading.c (freading): Likewise. * lib/fwriting.c (fwriting): Likewise. * lib/freadptr.c (freadptr): Likewise. * lib/freadseek.c (freadptrinc): Likewise. * lib/freadahead.c (freadahead): Likewise. * lib/fpurge.c (fpurge): Likewise. * lib/fseeko.c (rpl_fseeko): Likewise. * m4/fpending.m4 (gl_PREREQ_FPENDING): Add a variant for Plan9. Reported by Jens Staal <staal1978@gmail.com>.

--- a/lib/stdio-impl.h
+++ b/lib/stdio-impl.h
@@ -26,6 +26,8 @@
 # include <sys/param.h>
 #endif
 
+#include <errno.h>                             /* For detecting Plan9.  */
+
 #if defined __sferror || defined __DragonFly__ /* FreeBSD, NetBSD, OpenBSD, DragonFly, MacOS X, Cygwin */
 
 # if defined __DragonFly__          /* DragonFly */