kernel/linux: fix using custom location

Currently, extract and patch are skipped as thus:
- using a custom directory of pre-installed headers
- a correctly named directory already exists

Otherwise, extract and patch are done.

The current second condition is wrong, because it allows the following
sequence to happen:
- a non-custom kernel is used
- a previous build only partially extracted the non-custom sources
- that p[revious build broke during extraction (eg. incomplete tarball...)
- a subsequent build will find a properly named directory, and will
thus skip extract and patch, which is wrong

Fix that by following the conditions in this table:

Type | Extract | Patch
----------------------+---------+-------
Pre-installed headers | N | N
custom directory | N | N
custom tarball | Y | N
mainstream tarball | Y | Y

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: David Holsgrove <david.holsgrove@xilinx.com>

 diff -dur strace-4.5.16.orig/syscall.c strace-4.5.16/syscall.c

 --- strace-4.5.16.orig/syscall.c	2006-12-21 23:13:33.000000000 +0100

 +++ strace-4.5.16/syscall.c	2007-07-14 19:21:44.000000000 +0200

 @@ -1045,6 +1045,15 @@

  		/*

  		 * 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