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
As CPU_IS_LITTLE_ENDIAN is used nowehere except in test_libflac,
switch to CPU_IS_BIG_ENDIAN instead, which is actually used in the
code at several places. CMake didn't set the former but does set
the latter.
In 95e2c52 the autotools build worked fine, but CMake missed a few
defines. Activition of the lpc_compute_residual_from_qlp_coefficients
depended on encoder->private_->cpuinfo.use_asm for no reason, so
this dependency is removed
In some circles (Hydrogenaud.io for example) people share binaries
compiled from git, i.e. inbetween official releases. Files created
with these binaries cannot be discerned from others. To improve
troubleshooting, compiles from a git repository are marked with
the commit hash and date when configured with autotools or CMake
