Prior to this change, the pinelog benchmark suite was running as a
regular test, however, this is not ideal since it can result in timing
issues and giving false data to the runners.
This change explicitly marks them as benchmarks, so they can run using
`meson test --benchmark`
Meson is a far more robust build framework, compared to autotools. This
greatly simplifies adding new features, since it's far easier to
maintain a set of meson.build files vs the autotools mishmash.
DEPRECATION NOTICE: Autotools based build is deprecated and will be
removed in the future.
nirenjan