cargo{_common}.bbclass: abstract out parts for rustbuild

rustbuild is a cargo based way to build Rust but all of our helper bits
in cargo.bbclass would create a chicken/egg issue with dependencies
since we pull down pre-built binaries and use those for boot strapping.

classes/cargo_common.bbclass

@@ -0,0 +1,70 @@
+##
+## Purpose:
+## This class is to support building with cargo. It
+## must be different than cargo.bbclass because Rust
+## now builds with Cargo but cannot use cargo.bbclass
+## due to dependencies and assumptions in cargo.bbclass
+## that Rust & Cargo are already installed. So this
+## is used by cargo.bbclass and Rust
+##
+
+# add crate fetch support
+inherit crate-fetch
+inherit rust-common
+
+# Where we download our registry and dependencies to
+export CARGO_HOME = "${WORKDIR}/cargo_home"
+
+# The pkg-config-rs library used by cargo build scripts disables itself when
+# cross compiling unless this is defined. We set up pkg-config appropriately
+# for cross compilation, so tell it we know better than it.
+export PKG_CONFIG_ALLOW_CROSS = "1"
+
+cargo_common_do_configure () {
+	mkdir -p ${CARGO_HOME}
+	echo "paths = [" > ${CARGO_HOME}/config
+
+	for p in ${EXTRA_OECARGO_PATHS}; do
+		printf "\"%s\"\n" "$p"
+	done | sed -e 's/$/,/' >> ${CARGO_HOME}/config
+	echo "]" >> ${CARGO_HOME}/config
+
+	# Point cargo at our local mirror of the registry
+	cat <<- EOF >> ${CARGO_HOME}/config
+	[source.bitbake]
+	directory = "${CARGO_HOME}/bitbake"
+
+	[source.crates-io]
+	replace-with = "bitbake"
+	local-registry = "/nonexistant"
+	EOF
+
+	echo "[target.${HOST_SYS}]" >> ${CARGO_HOME}/config
+	echo "linker = '${RUST_TARGET_CCLD}'" >> ${CARGO_HOME}/config
+	if [ "${HOST_SYS}" != "${BUILD_SYS}" ]; then
+		echo "[target.${BUILD_SYS}]" >> ${CARGO_HOME}/config
+		echo "linker = '${RUST_BUILD_CCLD}'" >> ${CARGO_HOME}/config
+	fi
+}
+
+oe_cargo_fix_env () {
+	export CC="${RUST_TARGET_CC}"
+	export CXX="${RUST_TARGET_CXX}"
+	export CFLAGS="${CFLAGS}"
+	export CXXFLAGS="${CXXFLAGS}"
+	export AR="${AR}"
+	export TARGET_CC="${RUST_TARGET_CC}"
+	export TARGET_CXX="${RUST_TARGET_CXX}"
+	export TARGET_CFLAGS="${CFLAGS}"
+	export TARGET_CFLAGS="${CXXFLAGS}"
+	export TARGET_AR="${AR}"
+	export HOST_CC="${RUST_BUILD_CC}"
+	export HOST_CXX="${RUST_BUILD_CXX}"
+	export HOST_CFLAGS="${BUILD_CFLAGS}"
+	export HOST_CXXFLAGS="${BUILD_CXXFLAGS}"
+	export HOST_AR="${BUILD_AR}"
+}
+
+EXTRA_OECARGO_PATHS ??= ""
+
+EXPORT_FUNCTIONS do_configure