libcanfestival: fix several small build process issues

libcanfestival: fix several small build process issues

This patch tries to address the following package issues:

- the upstream hg repository seems to contain some invalid timestamps,
  at least the following warning are generated during package compilation
  (only one example):

  emcy.c: Timestamp out of range; substituting 2514-05-30 01:53:03.999999999

  This can be fixed by touching all files after unpacking, thus tar is
  now given the -m switch.

- one or more LEDE buildbot(s) do not have hg tool installed and thus are not
  able to checkout the sources from upstream

  This patch populates PKG_MIRROR_HASH in the hope that the buildbot's first
  try is to download an already packed source tarball prior to checkout it out
  from upstream.

- While at packaging from upstream, use the common infrastructure, i.e. use
  a source date etc. This also results in tar.xz files and thus reduces the
  disk footprint a little bit.

- during compilation the follwing warning could be observed:

  cc1: note: someone does not honour copts correctly, passed 0 times

  To silent down these warning, patch the Makefiles and pass the expected
  option.

Important note: changes are only compile tested due to missing hardware at
hand.

Signed-off-by: Michael Heimpold <mhei@heimpold.de>