rm_work: Improve handling for addto_recipe_sysroot

Rather than requiring each user to handle this individually, handle
addto_recipe_sysroot in the core class. As well as preserving the
sysroot directory, this also ensures the stamp is preserved rather
than rerunning the task every time as currently happens.

(From OE-Core rev: bf8b9858d9ccce27173d13938a83d249294cc473)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

meta/recipes-devtools/qemu/qemu-helper-native_1.0.bb

@@ -20,6 +20,5 @@ do_install() {
 	install tunctl ${D}${bindir}/
 }
 
-RM_WORK_EXCLUDE_ITEMS += "recipe-sysroot-native"
 DEPENDS += "qemu-native"
 addtask addto_recipe_sysroot after do_populate_sysroot before do_build