rust: use a shared source location for all the packages needing the rustc source tree

classes/shared-source-use.bbclass

@@ -0,0 +1,4 @@
+S = "${TMPDIR}/work-shared/${SOURCE_NAME}-${PV}-${PR}"
+
+do_configure[depends] += "${SOURCE_NAME}-source-${PV}:do_patch"
+do_populate_lic[depends] += "${SOURCE_NAME}-source-${PV}:do_unpack"