bin/xbps-checkvers: add -X flag to check and skip removed packages with existing revdeps

[Duncaen]

This should make the list of removed packages safer to use by not printing removals of packages with existing revdeps.

In the x86_64 repo is currently one package which would be skipped, showing that it works.

$ ./bin/xbps-checkvers/xbps-checkvers -d -eX >/dev/null
skipping: libprotobuf22-32bit: protobuf-devel-32bit-3.11.4_1 depends on it
skipping: libprotobuf22-lite-32bit: protobuf-devel-32bit-3.11.4_1 depends on it

The package (protobuf-devel-32bit-3.11.4_1) needs manual intervention, or some more logic in xbps-checkvers to notice that it should be removed (it was automatically generated, so there is no symlink, but since it was changed to a transitional package, the new -32bit package is not generated anymore).

[Duncaen]

@Chocimier

[Chocimier]

From past irc disscussion:

Chocimier> base-system depends on [virtual] awk, then we drop gawk and nawk, and make base-system [not depend on awk]
Chocimier> gawk and nawk will be removed before base-system is rebuild
duncaen> base-system depends on a specific awk implementation
duncaen> but I guess I can see the issue
duncaen> not planning to run it automatically after builds
duncaen> just to cleanup now and then instead of having to go through the list on 3 servers and delete things by hand
Chocimier> ship it then

Chocimier> [repodb]
duncaen> at least for install/updates I've found SAT solvers are not the best solution
duncaen> error messages are important and there are certain solutions that are prefferable
duncaen> and I guess a SAT solver might be a lot better at solving the whole database as compared to just a subset of things where you need to come up with one solution and not "there is one or more solutions"

[Duncaen]

Wouldn't xbps-repodb make this obsolete?

[Chocimier]

Yes it would, instead of xbps-checkvers -X | xargs rm; xbps-rindex -c one could do xbps-repodb; xbps-rindex -r.