eclass/wrapper: Add from gentoo

It's from gentoo commit f4a84c180c096ff27a077e3fc6475b99228ae9f9.

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

@@ -0,0 +1,59 @@
+# Copyright 1999-2020 Gentoo Authors
+# Distributed under the terms of the GNU General Public License v2
+
+# @ECLASS: wrapper.eclass
+# @MAINTAINER:
+# base-system@gentoo.org
+# @BLURB: create a shell wrapper script
+
+if [[ -z ${_WRAPPER_ECLASS} ]]; then
+_WRAPPER_ECLASS=1
+
+# @FUNCTION: make_wrapper
+# @USAGE: <wrapper> <target> [chdir] [libpaths] [installpath]
+# @DESCRIPTION:
+# Create a shell wrapper script named wrapper in installpath
+# (defaults to the bindir) to execute target (default of wrapper)
+# by first optionally setting LD_LIBRARY_PATH to the colon-delimited
+# libpaths followed by optionally changing directory to chdir.
+make_wrapper() {
+	local wrapper=$1 bin=$2 chdir=$3 libdir=$4 path=$5
+	local tmpwrapper="${T}/tmp.wrapper.${wrapper##*/}"
+	has "${EAPI:-0}" 0 1 2 && local EPREFIX=""
+
+	(
+	echo '#!/bin/sh'
+	if [[ -n ${libdir} ]] ; then
+		local var
+		if [[ ${CHOST} == *-darwin* ]] ; then
+			var=DYLD_LIBRARY_PATH
+		else
+			var=LD_LIBRARY_PATH
+		fi
+		cat <<-EOF
+			if [ "\${${var}+set}" = "set" ] ; then
+				export ${var}="\${${var}}:${EPREFIX}${libdir}"
+			else
+				export ${var}="${EPREFIX}${libdir}"
+			fi
+		EOF
+	fi
+	[[ -n ${chdir} ]] && printf 'cd "%s" &&\n' "${EPREFIX}${chdir}"
+	# We don't want to quote ${bin} so that people can pass complex
+	# things as ${bin} ... "./someprog --args"
+	printf 'exec %s "$@"\n' "${bin/#\//${EPREFIX}/}"
+	) > "${tmpwrapper}"
+	chmod go+rx "${tmpwrapper}"
+
+	if [[ -n ${path} ]] ; then
+		(
+		exeopts -m 0755
+		exeinto "${path}"
+		newexe "${tmpwrapper}" "${wrapper}"
+		) || die
+	else
+		newbin "${tmpwrapper}" "${wrapper}" || die
+	fi
+}
+
+fi