GitLab

This commit fixes all known floating-point bugs with the pico-sdk.  There
are two things going on here:
- Use a custom pico float component so that the pico-sdk doesn't include
  its math functions, and then provide our own from lib/libm.
- Provide a wrapper for __aeabi_fadd to fix the infinity addition bug.

Prior to this commit, the following tests failed on the rp2 port: cmath_fun
float_parse math_domain math_domain_special math_fun_special.  With this
commit, all these tests pass.

Thanks to @projectgus for how to approach this fix.
Signed-off-by: Damien George <damien@micropython.org>