rustlib: libdir may be different between build and host

With multilib, we may want to install under lib64 but the rust libraries
get published in the build sysroot under the libdir for the build
machine which is usually just lib. Support these being different.

recipes-devtools/rust/rustlib.bb

@@ -9,7 +9,7 @@ DEPENDS += "virtual/${TARGET_PREFIX}rust"
 RUSTLIB_DEP = ""
 
 do_install () {
-	for f in ${STAGING_DIR_NATIVE}/${rustlib}/*.so; do
+	for f in ${STAGING_DIR_NATIVE}/${rustlib_src}/*.so; do
 		echo Installing $f
 		install -D -m 755 $f ${D}/${rustlib}/$(basename $f)
 	done