Resolve build errors from Rust 1.55 upgrade

[scbrickley]

The Flux release into influxdb experienced some strange CI errors that we believe were caused by the upgrade to Rust version 1.55 in the Flux docker container.

#4038 downgraded the rust version back to 1.54 to unblock the release, but we will eventually want to go back to 1.55, once we figure out how to resolve these issues.

DOD:

• The flux docker container uses Rust 1.55
• We can release into influxdb without issue
• If we need the new math lib (aka -lm) to be linked lets make sure we understand why, possibly file Rust bug if this was a breaking change on their side.

[nathanielc]

Relevant comment about the current errors #4038 (comment)

[jsternberg]

Found in a Linux man page.

FMA(3)                                                           Linux Programmer's Manual                                                           FMA(3)

NAME
       fma, fmaf, fmal - floating-point multiply and add

SYNOPSIS
       #include <math.h>

       double fma(double x, double y, double z);
       float fmaf(float x, float y, float z);
       long double fmal(long double x, long double y, long double z);

       Link with -lm.

[fchikwekwe]

This is an interesting issue that is possibly related. rust-lang/rust#88817

[fchikwekwe]

Also, looking at the files that were failing the previous build, it looks like f32.rs and f64.rs are affected. There is a new linear interpolation method (lerp) in each file that references the intrinsics fmaf32 and fmaf64 respectively via the mul_add function. The direct use of the mul_add function and the import of these float types seem to be the reasons that we need the math library linked all of a sudden. This seems to be due to an inconsistency in how intrinsics are referenced as seen in the issue I linked in the previous comment.

[fchikwekwe]

Here's the f32 lerp method: https://github.com/rust-lang/rust/blob/master/library/std/src/f32.rs#L907
and the one for f64: https://github.com/rust-lang/rust/blob/master/library/std/src/f64.rs#L909