scripts/bootstrap-prefix: avoid USE=cet with binutils during bootstrap

the host compiler used may not support CET, causing binutils to fail, so
wait for that later when we got our own compiler

Thanks hsk17 for the analysis and proposed fix.

Bug: https://bugs.gentoo.org/936629
Signed-off-by: Fabian Groffen <grobian@gentoo.org>

scripts/bootstrap-prefix.sh

@@ -2027,6 +2027,10 @@ bootstrap_stage2() {
 		echo "sys-devel/gcc -pie" >> "${ROOT}"/tmp/etc/portage/package.use
 	fi
 
+	# don't use CET, we don't know if the host compiler supports it
+	echo "sys-devel/binutils -cet" >> \
+		"${ROOT}"/tmp/etc/portage/profile/package.use.force
+
 	emerge_pkgs --nodeps "${pkgs[@]}" || return 1
 
 	# Debian multiarch supported by RAP needs ld to support sysroot.