eclass/eqawarn: Add from Gentoo

It's from Gentoo commit c54b9fc0e02e07d4af019d81de611c865521b369.

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

@@ -0,0 +1,26 @@
+# Copyright 1999-2022 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+# @ECLASS: eqawarn.eclass
+# @MAINTAINER:
+# base-system@gentoo.org
+# @SUPPORTED_EAPIS: 6
+# @BLURB: output a QA warning
+
+case ${EAPI} in
+	6) ;;
+	*) die "${ECLASS}: EAPI ${EAPI:-0} not supported" ;;
+esac
+
+# @FUNCTION: eqawarn
+# @USAGE: [message]
+# @DESCRIPTION:
+# Proxy to ewarn for package managers that don't provide eqawarn and
+# use the PM implementation if available.  Reuses PORTAGE_ELOG_CLASSES
+# as set by the dev profile.
+if ! declare -F eqawarn >/dev/null ; then
+	eqawarn() {
+		has qa ${PORTAGE_ELOG_CLASSES} && ewarn "$@"
+		:
+	}
+fi