Can't use `f32` transcendental functions (`sin`, `cos`) because lto `fat` is broken in rust 1.66

[bunnie]

Rust 1.66 breaks lto fat due to a panic inside sin()/cos() routines.

This issue is to investigate this further. Two options:

1. Create pure Rust versions of sin/cos that don't break in LTO
2. Pull out the entire FFT analysis routine and do it on the tester host side

2 is probably the better outcome but definitely a lot more work and risk on production quality.

[bunnie]

Note: Losing fat and going to thin adds 600kiB to the Xous binary size

[bunnie]

Did some investigations.

• see if mold can work with this - yes, but: can't handle custom kernel link.x script (not a feature of mold), requires PIC, which isn't enabled in current std, thus would require a patch to std that could cause it to not be upstreamable. aborting approach. Note build time of services goes from 28s to 20s, so about 30% improvement with mold.
• see if gold can work with this - NO, gold is bit-rotted and does not support risc-v
• see if ld can work with this xobs found that the bug still exists (see image below)

Seems like we have to wait for llvm to fix this.

Next step: try to excise out the one broken function, or maybe it can be bodged around in some way...

[bunnie]

lto fat restored in 79be209 because I have gone through and eliminated calls to f32::cos() through the entire system and replaced it with a less-accurate, but more compact and more importantly not crashing quadrant table-lookup based cosine implementation.

The llvm issue is still real. Renaming the bug and leaving it open to remind ourselves to revisit the issue someday if the llvm issue (rust-lang/rust#105734) ever gets fixed, especially if users eventually want to use cos(), sin(), etc.