linux: userspace GPIO control

Allow use host GPIO pins for non-realtime purposes.

Signed-off-by: Andrey Kunitsyn <blackicebox@gmail.com>

src/linux/internal.h

@@ -11,6 +11,7 @@
 // console.c
 void report_errno(char *where, int rc);
 int set_non_blocking(int fd);
+int set_close_on_exec(int fd);
 int console_setup(char *name);
 void console_sleep(struct timespec ts);