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>

 # Build script for m4

 CT_M4_VERSION=1.4.13

 do_companion_tools_m4_get() {

     CT_GetFile "m4-${CT_M4_VERSION}" \

                {ftp,http}://ftp.gnu.org/gnu/m4

 }

 do_companion_tools_m4_extract() {

     CT_Extract "m4-${CT_M4_VERSION}"

     CT_Patch "m4" "${CT_M4_VERSION}"

 }

 do_companion_tools_m4_build() {

     CT_DoStep EXTRA "Installing m4"

     mkdir -p "${CT_BUILD_DIR}/build-m4"

     CT_Pushd "${CT_BUILD_DIR}/build-m4"

     CT_DoExecLog CFG \

     "${CT_SRC_DIR}/m4-${CT_M4_VERSION}/configure" \

         --prefix="${CT_BUILDTOOLS_PREFIX_DIR}"

     CT_DoExecLog ALL make

     CT_DoExecLog ALL make install

     CT_Popd

     CT_EndStep

 }