Disabled separate 32-bit and GNU C++ builds for CI. For most jobs also
disabled building examples and self-contained header tests. For UBSan
jobs enabled global visibility in attempt to work around the bogus
errors about calling virtual functions through a pointer to a base class.
Boost.Log tests include compilation of all examples, so depinst needs
to pull dependencies of examples, in addition to the library itself and
its tests.
Also, added --jobs argument to the `git submodule update` executed by
depinst and increased the number of jobs to 8.
