build: fix duplicate building of host-tools

Upstream introduced two different methods for determining the state of a
package within the OpenWrt buildsystem. While both are based around the
md5 hash-function, one taks filename & mtime into account while the
other one uses the actual md5 hash of the file-content.

Ever wondered why Gluon suddenly took considerably longer to build?
The messy part is how the build-system chooses which method to use. This
is based around the AUTOREMOVE configuration. Gluon sets this variable
conditionally when built with GLUON_AUTOREMOVE set to 1.

Enter the Gluon build-system. It first compiles Lua, without the
AUTOREMOVE configuration passed to OpenWrt. This compiles the packages
with the old hash-method based around filename & mtime. Afterwards, it
builds with AUTOREMOVE enabled, changing the hash-function and
rebuilding all host-packages.

Fix this by setting AUTOREMOVE for both build-processes according to the
setting of GLUON_AUTOREMOVE.

Link: https://github.com/openwrt/openwrt/commit/53a08e37437972ba0a8fbf953a93a70a6b784ef4



Signed-off-by: David Bauer <mail@david-bauer.net>