Move last remaining module from std.c and remove a reference to Windows in core.sys.posix
Extend unittest for ldexp()

The unit test checks some edge cases for 80bit reals.
This pull request adds a test for platforms which only have 64bit reals (e.g. ARM, PPC).
Merge pull request #1008 from redstar/math

Extend unittest for ldexp()
Merge pull request #1007 from joakim-noah/move_winsock

Move last remaining module from std.c
use naked asm blocks to clear registers
fix Issue 12800 - Fibers are broken on Win64

- save non-volatile registers RSI and RDI