staging: Use relative path in sysroot-destdir for target recipes

Original we used absolute path in sysroot-destdir for both native and
target recipes. This commit changes target recipes to use relative path
which is same as the image directory.

[sgw: merged with libtool sysroot work]
Signed-off-by: Dongxiao Xu <dongxiao.xu@intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>

meta/classes/cross.bbclass

@@ -50,6 +50,8 @@ base_sbindir = "${bindir}"
 libdir = "${exec_prefix}/lib/${MULTIMACH_TARGET_SYS}"
 libexecdir = "${exec_prefix}/libexec/${MULTIMACH_TARGET_SYS}"
 
+do_populate_sysroot[sstate-inputdirs] = "${SYSROOT_DESTDIR}/${STAGING_DIR_NATIVE}"
+
 do_install () {
 	oe_runmake 'DESTDIR=${D}' install
 }