systemd: use AC_CHECK_TOOL instead of AC_PATH_TOOL when checking objcopy, strings, gperf
* with external toolchain I have different HOST_PREFIX and HOST_SYS
AC_PATH_TOOL is using HOST_SYS as prefix and fails to find objcopy
then it tries objcopy without prefix which is found on host, but
that objcopy does not work for arm libs
* with internal toolchain gperf is not prefixed with HOST_PREFIX, but
fallback to "gperf" only finds the one in native sysroot first
* based on http://lists.linuxtogo.org/pipermail/openembedded-core/2013-April/037985.html
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
