Coverage builds need to be special cased since they aren't specified
in sanitizers. Instead they are done for all C/C++ projects that
use libFuzzer.
Move all of this special casing to `should_build_coverage` and call that from
`should_build` so we have one place where we decide this.
Add tests as well.
Fixes: https://github.com/google/oss-fuzz/issues/4371
* [util-linux] cover mnt_table_parse_stream
Waiting for https://github.com/karelzak/util-linux/pull/1068
* temporarily point OSS-Fuzz to evverx/util-linux
* make sure it can be built with sanitizer=coverage
jonathanmetzman