Parse enough of config.yaml to auto-generate config.auto.h and config.auto.c.
This commit implements most of the infrastructure needed to migrate the rest of the build code to C, but each set of auto-generated files will present its own challenges.
The build is now dependent on libyaml. At this point there is no need for a hard requirement, but that will come soon so it seems better to add the dependency now.
Update Ubuntu 12.04 to 16.04. Version 16.04 is recently EOL but testing on an old version is beneficial.
Update Ubuntu 18.04 to 20.04.
Update Fedora 32 to 33. Version 34 would have been preferred but there were some build issues, i.e. the default shell did not work with configure, and after ksh was installed configure locked up.
Add --no-install-recommends to apt-get commands to save a bit of time and space.
Update test Dockerfile to run in multiple steps. This makes the container larger but also makes rebuilding after changes faster. The --squash option may be used to keep the container small.
Remove obsolete casts in protocol/parallel module. These casts were included in the original migration because Ubuntu 12.04 32-bit gcc required them, but Ubuntu 16.04 32-bit gcc complains. There is no production issue here since at this point in the code the file descriptors are guaranteed to be >= 0.
The CentOS 7 documentation test relies on PostgreSQL 9.5 which has been removed from the yum.p.o repository package. Switch the test to CentOS 8 to fix the immediate issue, but a decision on the PostgreSQL 9.5 documentation will need to be made before the next release.
Testing on Travis-CI has been getting slower (from ~18 minutes to 3-6 hours) and the travis-ci.org service will be terminated at the end of the year. Moving to travis-ci.com is an option but the quotas are too low for our purposes.
Instead use Github Actions, which does not currently have quotas, and runs our current tests with just a few tweaks.
This still leaves multi-architecture tests on Travis-CI but we may be able to run those and stay within the new quotas.
Also fix a minor bug in restoreTest.c exposed by Github Actions using a different name for the user and group.
