Make the Individual tests linkable for meson

- In the current state, the tests can only be linkable
  together into a single binary, as we are using the few
  vaiables from external tests and using them during link
  time to generate the executable.

- The idea of this commit is to make the unit test files
  linkable individually, so that we have have a better way
  of running unitests through meson, rather than bundling all
  the tests into a gaigantic binary.

TestedBy:
The unit tests are passed in CI

Signed-off-by: Manojkiran Eda <manojkiran.eda@gmail.com>
Change-Id: I67b953e5bc227d876139373aebeacbf5c20f56ef
5 files changed