scripts: remove . from $PATH

Add CT_SanitizePath function which removes entries referring to ., /tmp
and non-existing directories from $PATH, and call it early in the
build script.

If . is in PATH, gcc-4.4.4 build breaks:

[ALL ] checking what assembler to use...
/tmp/build/targets/arm-unknown-linux-uclibcgnueabi/build/gcc-core-static/arm-unknown-linux-uclibcgnueabi/bin/as
...
[ALL ] config.status: creating as

i.e. "as" is supposed to be the arm-unknown-linux-uclibcgnueabi cross assembler,
but config.status creates a local "as" script which is calling the
host assembler.

Signed-off-by: Johannes Stezenbach <js@sig21.net>
[Yann E. MORIN: style fixes + explanations]
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

# Build script for libtool

CT_LIBTOOL_VERSION=2.2.6b

do_companion_tools_libtool_get() {

    CT_GetFile "libtool-${CT_LIBTOOL_VERSION}" \

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

}

do_companion_tools_libtool_extract() {

    CT_Extract "libtool-${CT_LIBTOOL_VERSION}"

    CT_Patch "libtool" "${CT_LIBTOOL_VERSION}"

}

do_companion_tools_libtool_build() {

    CT_DoStep EXTRA "Installing libtool"

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

    CT_Pushd "${CT_BUILD_DIR}/build-libtool"

    CT_DoExecLog ALL \

    "${CT_SRC_DIR}/libtool-${CT_LIBTOOL_VERSION}/configure" \

        --prefix="${CT_TOOLS_OVERIDE_DIR}"

    CT_DoExecLog ALL make

    CT_DoExecLog ALL make install

    CT_Popd

    CT_EndStep

}