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 -durN strace-4.5.19.orig/syscall.c strace-4.5.19/syscall.c

 --- strace-4.5.19.orig/syscall.c	2009-10-12 21:54:21.000000000 +0200

 +++ strace-4.5.19/syscall.c	2009-10-28 18:47:18.000000000 +0100

 @@ -1022,6 +1022,15 @@

  		/*

  		 * Note: we only deal with only 32-bit CPUs here.

  		 */

 +

 +		if (!(tcp->flags & TCB_INSYSCALL) &&

 +		    (tcp->flags & TCB_WAITEXECVE)) {

 +			/* caught a fake syscall from the execve's exit */

 +			tcp->flags &= ~TCB_WAITEXECVE;

 +			return 0;

 +		}

 +

 +

  		if (regs.ARM_cpsr & 0x20) {

  			/*

  			 * Get the Thumb-mode system call number