Fix an off-by-one bug in ar71xx_gpio and bcm2835_gpio which makes the last
pin unavailable.

Reported and tested by:	sbruno (ar71xx)
Approved by:	adrian (mentor)
Pointy hat to:	loos
Remove the hardcoded limit for the number of gpio_pins that can be used.
Allocate it dynamically.

Approved by:	adrian (mentor)
libc: Make resolver sockets close-on-exec (SOCK_CLOEXEC).

Although the resolver's sockets are exposed to applications via res_state,
I do not expect them to pass the sockets across execve().