eclass/crossdev: Add from Gentoo

It's from Gentoo commit 00ee14eab35e0dad294da8efe1c9f6606c3e4794.

sdk_container/src/third_party/portage-stable/eclass/crossdev.eclass

@@ -0,0 +1,77 @@
+# Copyright 1999-2023 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+# @ECLASS: crossdev.eclass
+# @MAINTAINER:
+# cat@catcream.org
+# @AUTHOR:
+# Alfred Persson Forsberg <cat@catcream.org> (21 Jul 2023)
+# @SUPPORTED_EAPIS: 7 8
+# @BLURB: Convenience wrappers for packages used by the Crossdev tool.
+
+inherit toolchain-funcs
+
+case ${EAPI} in
+	7|8) ;;
+	*) die "${ECLASS}: EAPI ${EAPI:-0} not supported" ;;
+esac
+
+if [[ -z ${_CROSSDEV_ECLASS} ]]; then
+_CROSSDEV_ECLASS=1
+
+# @ECLASS_VARIABLE: _CROSS_CATEGORY_PREFIX
+# @INTERNAL
+# @DESCRIPTION:
+# This variable specifies the category prefix for a Crossdev
+# package. For GCC Crossdev it is "cross-", and for LLVM it is
+# "cross_llvm-"
+_CROSS_CATEGORY_PREFIX=""
+
+# @ECLASS_VARIABLE: _IS_CROSSPKG_LLVM
+# @INTERNAL
+# @DESCRIPTION:
+# Is true if the package is in a LLVM Crossdev category, otherwise false
+_IS_CROSSPKG_LLVM=0
+if [[ ${CATEGORY} == cross_llvm-* ]] ; then
+	_IS_CROSSPKG_LLVM=1
+	_CROSS_CATEGORY_PREFIX="cross_llvm-"
+fi
+
+# @ECLASS_VARIABLE: _IS_CROSSPKG_GCC
+# @INTERNAL
+# @DESCRIPTION:
+# Is true if the package is in a GCC Crossdev category, otherwise false
+_IS_CROSSPKG_GCC=0
+if [[ ${CATEGORY} == cross-* ]] ; then
+	_IS_CROSSPKG_GCC=1
+	_CROSS_CATEGORY_PREFIX="cross-"
+fi
+
+# @ECLASS_VARIABLE: _IS_CROSSPKG
+# @INTERNAL
+# @DESCRIPTION:
+# Is true if the package is in a any Crossdev category, otherwise false
+[[ ${_IS_CROSSPKG_LLVM} == 1 || ${_IS_CROSSPKG_GCC} == 1 ]] && _IS_CROSSPKG=1
+
+# Default CBUILD and CTARGET to CHOST if unset.
+export CBUILD=${CBUILD:-${CHOST}}
+export CTARGET=${CTARGET:-${CHOST}}
+
+if [[ ${CTARGET} == ${CHOST} ]] ; then
+	# cross-aarch64-gentoo-linux-musl -> aarch64-gentoo-linux-musl
+	[[ ${_IS_CROSSPKG} == 1 ]] && export CTARGET=${CATEGORY#${_CROSS_CATEGORY_PREFIX}}
+fi
+
+# @FUNCTION: target_is_not_host
+# @RETURN: Shell true if we're targeting an triple other than host
+target_is_not_host() {
+	 [[ ${CHOST} != ${CTARGET} ]]
+}
+
+# @FUNCTION: is_crosspkg
+# @RETURN: Shell true if package belongs to any crossdev category
+is_crosspkg() {
+	 [[ ${_IS_CROSSPKG} == 1 ]]
+}
+
+fi