os-windows: fix cpumask operations

os-windows: fix cpumask operations

Fix cpumask manipulation on (64-bit) Windows systems.

cpus_allowed=nn values greater than 32 does not work, due to
* the compiler not promoting expressions like "1 << cpu" to
  64 bits
* the clear function clearing the wrong bit (using "cpu - 1"),
* the clear function using XOR to clear (which only works if the
  bit was previously set)
* the check function returning a 64-bit value through a 32-bit
  return value

Example problems (from extra debug prints):
* setting CPU 32 really sets bit 0 (CPU 0)
	Set mask of 0000000000000000 to add 0000000000000001 (32)

* setting CPU 63 really sets bit 31 (CPU 31)
	Set mask of 0000000000000000 to add 0000000080000000 (63)

* clearing CPU 0 really clears bit 63 (CPU 63)
	Clear mask of 0000000055555555 to remove 8000000000000000 (0)

* clearing CPU 2 really clears bit 2 (CPU 2)
	Clear mask of 0000000055555555 to remove 0000000000000002 (2)

* checking claims CPU 32 is not in a mask of CPUs {32,34,36,38}
	for 0000005500000000 check if bit 32 is set ==> FALSE

Tested with x86_64-w64-mingw32-gcc 6.4.0 from cygwin on a system
with 64 CPU cores (all fitting in one Windows processor group).

Signed-off-by: Jens Axboe <axboe@kernel.dk>