xbps-src: new layout in masterdir to use a common directory from host.

XBPS_CACHEDIR has been replaced by XBPS_HOSTDIR in configuration file,
and this expects the following structure:

/host
  |_ /build (previously /pkg-builddir)
  |_ /binpkgs (previously /pkg-binpkgs)
  |_ /repocache (previously /cachedir)
  |_ /sources (previously /pkg-srcdistdir)

Thanks to str1ngs for the great idea!

xbps-src/shutils/chroot.sh.in

@@ -25,7 +25,7 @@
 
 _mount()
 {
-	MASTERDIR="${XBPS_MASTERDIR}" CACHEDIR="${XBPS_CACHEDIR}" \
+	MASTERDIR="${XBPS_MASTERDIR}" HOSTDIR="${XBPS_HOSTDIR}" \
 		${sudo_cmd} \
 		@@XBPS_INSTALL_LIBEXECDIR@@/xbps-src-chroot-helper mount
 	return $?
@@ -33,7 +33,7 @@ _mount()
 
 _umount()
 {
-	MASTERDIR="${XBPS_MASTERDIR}" CACHEDIR="${XBPS_CACHEDIR}" \
+	MASTERDIR="${XBPS_MASTERDIR}" HOSTDIR="${XBPS_HOSTDIR}" \
 		${sudo_cmd} \
 		@@XBPS_INSTALL_LIBEXECDIR@@/xbps-src-chroot-helper umount
 	return $?
@@ -86,8 +86,8 @@ _EOF
 	if [ -n "$XBPS_COMPRESS_LEVEL" ]; then
 		echo "XBPS_COMPRESS_LEVEL=$XBPS_COMPRESS_LEVEL" >> $XBPSSRC_CF
 	fi
-	if [ -n "$XBPS_CACHEDIR" ]; then
-		echo "XBPS_CACHEDIR=/cachedir" >> $XBPSSRC_CF
+	if [ -n "$XBPS_HOSTDIR" ]; then
+		echo "XBPS_HOSTDIR=/host" >> $XBPSSRC_CF
 	fi
 
 	echo "# End of configuration file." >> $XBPSSRC_CF