Remove global -ffast-math flag, instead apply fast math to just color_helpers.cpp

[sharkautarch]

Should fix https://github.com/ValveSoftware/gamescope/issues/1493

[misyltoad]

I'd rather just have the pragma thing, rather than the denorms thing... We can come back to it if we want it.

[sharkautarch]

@Joshua-Ashton instead of turning on ftz/daz globally, I ended up using some intrinsics for x86 and aarch64 to just turn on ftz/daz inside calcColorTransform create_color_mgmt_luts, w/ the msrs being restored after returning from the function Let me know if this is ok, or just too complicated

[Exotic0015]

Can confirm this fixes #1493.

[sharkautarch]

Edited to remove the msr things as per misyl’s feedback