[ffmpeg] x86 build relying on nasm instead of yasm

[Baklap4]

Is your feature request related to a problem? Please describe.
It always bugs me when 2 tools are used for the same job. More tools come with more maintenance and should be avoided. Back in January 06c622e this was introduced to the ffmpeg port (#14547) as there was an issue with the linking phase:

LD libavcodec/avcodec-58.dll
Creating library libavcodec/avcodec.lib and object libavcodec/avcodec.exp
LINK : fatal error LNK1000: unknown error at 00007FF6F720AC26; consult documentation for technical support options

In which @mcmtroffaes proposed to keep on using yasm as for now on x86 builds

I've done a fresh rebase and spent some time trying to diagnose this problem. For me, on the 32 bit build, the linker just hangs for a really long time (like 20 minutes) at the avcodec linking stage, and then causes the powershell terminal to crash, but I suppose it's the same error. Not sure where to go from here, except to fall back on yasm for x86... 😕 I will add a commit to this effect.

A related issue to this is that for about 6 days the certificate of yasm was expired and thus failing builds see #19121 and #7379

Proposed solution
Either use yasm or nasm
When nasm is used figure out why the linking phase takes so long and fix that problem.

Describe alternatives you've considered
None

Additional context
I've tested the build with nasm yesterday (2021-08-10) with the then latest master which still ended up taking quite a while 'hanging' at the linking phase as described in the ffmpeg issue

@mcmtroffaes did you ever find out why it hangs on nasm in the linker phase? I was wondering if this commit was still needed in latest master. But It seems i'm running in the same problem that it just 'hangs' and doesn't do anything with nasm. I came here because of #19121 as yasm cannot be retrieved due to certificate error.

in which @mcmtroffaes replied saying he never really figured it out why it happens.

Documentation on how to build on windows: https://github.com/FFmpeg/FFmpeg/blob/master/doc/platform.texi#L98-L264

[BillyONeal]

I think we would prefer nasm because yasm has known memory corruption bugs and have not done an official release in a long time; it's part of why vcpkg builds yasm rather than using an existing copy.

[JackBoosY]

We hope your question was answered to your satisfaction; if it wasn't, you can reopen with more info.

[Baklap4]

Any link to an issue why nasm hangs upon building so further discussion can be done there?