Fix asn1c warnings.

The strategy is rather basic. Files with warnings are replaced
by an edited copy that triggers no warning.

We take care to check that the replaced file is the same as the
one that was analyzed at the time of warning removal (through
checking its SHA1).

There is a new bash script "fix_asn1" in cmake_targets/tools
and the files replacing the existing ones are in
cmake_targets/tools/fix_asn1.data.