configure: add possibility to set arbitrary variable in check_for

If check_for is able to find the required prog/inc/lib, allow it to
set an arbitrary variable to 'y'. This variable is then pushed down
to the kconfig definition.

For example:
has_or_abort prog=foobar kconfig=has_foobar

If foobar is available, it yields a kconfig variable defaulting to y:
config CONFIGURE_has_foobar
bool
default y

If foobar is missing, it yields a kconfig variable defaulting to n:
config CONFIGURE_has_foobar
bool

Thus it is possible to depends on that variabel to show/hide options:
config SOME_FEATURE
bool
prompt "Some feature"
depends on CONFIGURE_has_foobar

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

diff -Narup uClibc-0.9.30.1.orig/libc/inet/getaddrinfo.c uClibc-0.9.30.1/libc/inet/getaddrinfo.c

--- uClibc-0.9.30.1.orig/libc/inet/getaddrinfo.c	2009-02-26 21:49:14.000000000 +0900

+++ uClibc-0.9.30.1/libc/inet/getaddrinfo.c	2009-03-06 00:59:23.000000000 +0900

@@ -187,6 +187,8 @@ static unsigned __check_pf(void)

 		}

 		for (runp = ifa; runp != NULL; runp = runp->ifa_next) {

+			if (runp->ifa_addr == NULL)

+				continue;

 #if defined __UCLIBC_HAS_IPV4__

 			if (runp->ifa_addr->sa_family == PF_INET)

 				seen |= SEEN_IPV4;