[FEATURE] Compiler flags like -march and -03, possibly others

[Stryxus]

linux-tkg has the ability to set -march=(znver3) and other flags like -03. I see these scattered about in the proton-tkg.sh. Would it be possible to carry the ability of setting these over to proton? It would be interesting to see if these have any benefits since if they do in linux-tkg enough to justify them being their own settings, I would think they would here too. CachyOS proton does this but they are only prebuild per x86_64 version.

[mikeserv-git]

You have to be careful what instructions you enable. I do it, but there are places where I unset and reset reset flags to something saner (DXVK, vkd3d-proton, the valve stuff). If you use -march with a cpu type that allows the compiler to turn on AVX instructions for DXVK and vkd3d-proton you may subtly break them. What happened for me was that any game that actually USED the AVX/AVX2 instructions immediately crashed. I thought it was OK at first until I actually hit that.