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.

classes/rust-bin.bbclass

@@ -36,7 +36,11 @@ OVERLAP_DEPS = "${@get_overlap_deps(d)}"
 # See https://github.com/rust-lang/rust/issues/19680
 RUSTC_FLAGS += "-C prefer-dynamic"
 
-rustlib="${libdir}/${TUNE_ARCH}${TARGET_VENDOR}-${TARGET_OS}/rustlib/${HOST_SYS}/lib"
+rustlib_suffix="${TUNE_ARCH}${TARGET_VENDOR}-${TARGET_OS}/rustlib/${HOST_SYS}/lib"
+# Native sysroot standard library path
+rustlib_src="${prefix}/lib/${rustlib_suffix}"
+# Host sysroot standard library path
+rustlib="${libdir}/${rustlib_suffix}"
 CRATE_NAME ?= "${@d.getVar('BPN', True).replace('-rs', '').replace('-', '_')}"
 BINNAME ?= "${BPN}"
 LIBNAME ?= "lib${CRATE_NAME}-rs"