Close #5019
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

In practice, this probably will not link properly even if the
pkg-config --static parameter is forced, except on Windows.

Unfortunately, we cannot emit NEON opcodes when NEON is not explicitly
enabled (-mfpu=neon), contrary to MMX & SSE on x86. As a consequence,
this will not work for inline assembler in a non-optimized plugin,
namely the deinterlacer.

There is also a(n hopefully theoretical) bug whereby the compiler would
emit NEON instructions in the descriptor or activation callback of a
NEON plugin. This could then crash if NEON is not supported, even
before the NEON run-time check is reached.

'make fetch' has to fetch sources for all the built packages,
including dependency packages. Conversely, 'make fetch' should not
fetch sources of distro-provided packages, not even dependencies.
This should fix that.

As an minor bonus, 'make .foo' should now work even if foo is
provided by the distro, and conditional build rules should be cleaner.

Remove the old way with using the static makefiles and weird ??PREFIX?? patches

Same, not libav* enabled