On some platforms, e.g. FreeBSD, there is a requirement to allow the user to disable support for features even when the required library is present.
Introduce tri-state options for the optional features: auto mimics the current behavior and is the default, enable requires libraries for the feature to be present, and disable disables the feature without checking the libraries.
Meson has a lot of advantages over autoconf/make, primarily in ease-of-use and performance. Make meson the only build system used for testing and building the Debian documentation, but leave the RHEL documentation using autoconf/make for now so it gets some testing.
This is immediately useful because it will detect any extern'd functions or variables that are not being used. It also detects functions or variables that are declared but not defined.
If a FV/VR_EXTERN macro is missing it will be detected either because of a mismatch in the declaration/definition or because a new defined symbol will appear in the nm test.
Eventually the unity build will be used to create a more optimized pgbackrest binary but that will need to wait.
Meson is a new build system that offers simpler syntax and superior performance to autoconf/make. In addition, Windows is supported natively.
The Meson build appears complete, but currently is used only for auto-generation of code and the host build of pgbackrest. Some container upgrades will be required before Meson can be used for container builds.
Also patch the Debian package to force autoconf/make rather than Meson.
