binutils: add comment

srcpkgs/binutils/template

@@ -47,7 +47,7 @@ do_configure() {
 	if [ "$CROSS_BUILD" ]; then
 		# we don't want --with-sysroot=${XBPS_CROSS_BASE} like gnu-configure
 		conf+=" --host=${XBPS_CROSS_TRIPLET} --with-build-sysroot=${XBPS_CROSS_BASE}"
-
+		# pkgconf adds sysroot includes to cflags and ldflags, which breaks binutils cross-compile with zstd
 		vsed -e '/PKG_CONFIG_SYSROOT_DIR/d' -i ${XBPS_WRAPPERDIR}/${XBPS_CROSS_TRIPLET}-pkg-config
 	fi