As it turns out that the PPC-specific code provides no benefit with
modern, autovectorizing compilers, and given that there is a lot of
cruft surrounding the PPC-specific parts, remove all of it.
See also https://lists.xiph.org/pipermail/flac-dev/2022-December/006620.html
* Improve CPU features detection
CMAKE_SYSTEM_PROCESSOR is pretty useless (e.g. when compiling with
MSVC ARM64 toolchain and Ninja still returns system processor).
* Don't build src/utils targets by default
Fix compilation for UWP platform.
* Add more Visual studio Git ignore patterns
* Autogenerate Doxygen docs