mdns-repeater: pass through CFLAGS/LDFLAGS and package version

mdns-repeater: pass through CFLAGS/LDFLAGS and package version

Before the change, the feed Makefile would not rely on the predefined
logic of building Makefile-based packages, rather it defined its own
`Build/Compile` step that explicitly called `make`. This didn't play
along well with the upstream Makefile, which doesn't respect the CFLAGS
that come from the environment.

The effect of that was that, for example, `CONFIG_PKG_ASLR_PIE_ALL=y`
was not respected: a non-PIE binary was generated regardless. Other
compiler flags were ignored too in the same manner.

Also it would try to determine the mdns-repeater version by calling to
git, which wouldn't work, since the build system downloaded a pre-made
source tarball without a bundled `.git` directory. The result is an
empty version string when calling `mdns-repeater -h`.

To address all of the above, switch to the built-in logic for
Makefile-type projects. Append to MAKE_FLAGS to completely override
upstream CFLAGS/LDFLAGS and pass through the package version. Set a
dummy HGVERSION variable value to prevent the upstream Makefile from
calling `git` unnecessarily.

Signed-off-by: Foster Snowhill <redacted>