clean up some common definitions across rust versions

These bits and pieces had evidently been copy-pasted forward into each
new recipe version, but now they are all identical and can be tidied up.

recipes-devtools/rust/libstd-rs.inc

@@ -2,6 +2,7 @@ SUMMARY = "Rust standard libaries"
 HOMEPAGE = "http://www.rust-lang.org"
 SECTION = "devel"
 LICENSE = "MIT | Apache-2.0"
+LIC_FILES_CHKSUM = "file://../../COPYRIGHT;md5=93a95682d51b4cb0a633a97046940ef0"
 
 RUSTLIB_DEP = ""
 inherit cargo
@@ -12,7 +13,9 @@ RUSTFLAGS += "-L ${STAGING_LIBDIR} -C link-arg=-Wl,-soname,libstd.so"
 
 S = "${RUSTSRC}/src/libstd"
 
+CARGO_FEATURES ?= "panic-unwind backtrace"
 CARGO_BUILD_FLAGS += "--features '${CARGO_FEATURES}'"
+CARGO_VENDORING_DIRECTORY = "${RUSTSRC}/vendor"
 
 do_compile_prepend () {
     export CARGO_TARGET_DIR="${B}"