sys-libs/zlib: fix mingw-w64 build.

Gentoo-Bug: https://bugs.gentoo.org/605484

Package-Manager: Portage-2.3.5, Repoman-2.3.2
Closes: https://github.com/gentoo/gentoo/pull/4662

sys-libs/zlib/zlib-1.2.11.ebuild

@@ -29,6 +29,13 @@ src_prepare() {
 		cd contrib/minizip || die
 		eautoreconf
 	fi
+
+	case ${CHOST} in
+	*-mingw*|mingw*)
+		# uses preconfigured Makefile rather than configure script
+		multilib_copy_sources
+		;;
+	esac
 }
 
 echoit() { echo "$@"; "$@"; }