We're getting there :)

and define the macros to force using the static version

This version makes sure pthreads-w32 isn't accidentally detected
and enabled; previously when building contribs for windows, aom
would end up trying to use pthreads-w32 (but fail linking the plugin)
if it was built after pthreads-w32.

This version also supports building with assembly or intrinsics
for windows on arm/arm64.

In principle, the same issue also exists in libvpx. However, when
libvpx is built with the contribs build system, the contribs include
directory isn't passed to libvpx, so it won't accidentally find
pthreads-w32. (This issue is fixed in the latest git version of libvpx.)

This makes sure it is updated properly if changing the hash used.

According to https://www.gnu.org/software/make/manual/html_node/Options_002fRecursion.html#index-recursion_002c-and-_002dj
"the parent make and all the sub-makes will communicate to ensure that there
are only ‘N’ jobs running at the same time between them all."

This avoids trying to use any assembler optimizations there; enabling
that requires a bit more patching.

This fixes building aom for armv7 and aarch64 with llvm-mingw.

The codec was officially announced, and is almost finished.

This should not be BP to stable until there is an official release of
the bitstream and the software. But it can help to test, for now.

The custom "configure" build system is slated to be dropped.
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>

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