util-linux: fix switch_root(8) with musl.

glibc declares some defs internally for struct dirent, _DIRENT_HAVE_D_TYPE
one of them. switch_root(8) expects this to be defined to properly remove
all subdirs stored in current root before switching.

This fixes those annoying warnings seen with musl on the initramfs.

srcpkgs/util-linux/template

@@ -1,7 +1,7 @@
 # Template file for 'util-linux'
 pkgname=util-linux
 version=2.27
-revision=1
+revision=2
 short_desc="Miscellaneous linux utilities"
 maintainer="Juan RP <xtraeme@voidlinux.eu>"
 homepage="https://www.kernel.org/pub/linux/utils/util-linux/"
@@ -23,6 +23,9 @@ conf_files="
 	/etc/pam.d/login"
 provides="eject-${version}_1"
 
+# XXX musl needs this for switch_root(8).
+CFLAGS="-D_DIRENT_HAVE_D_TYPE"
+
 pre_configure() {
 	NOCONFIGURE=1 ./autogen.sh
 }