This is really a few more-or-less separate changes:
* Remove all math aliases that were used in Go 1.16 and below (the
math.[A-Z] aliases).
* Replace math aliases with an assembly implementation (the math.arch*
aliases) with a LLVM intrinsic, where one is available.
* Include missing math functions in picolibc build.
This leaves just four math aliases:
* math.archHypot and math.archModf do not have a LLVM builtin
equivalent. They could be replaced with calls to libm, and I think
that would be a good idea in the long term.
* math.archMax and math.archMin do have a LLVM builtin equivalent
(llvm.maximum.f64, llvm.minimum.f64), but unfortunately they crash
when used. Apparently these exact operations are not yet widely
supported in hardware and they don't have a libm equivalent either.
There are more LLVM builtins that we could use for the math package
(such as FMA), but I will leave that to a future change. It could
potentially speed up some math operations.
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