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).
More @safe-ty for core.sync
Merge pull request #1009 from Dicebot/sync-safety

More @safe-ty for core.sync
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