Revert "Do not use a global variable in coroutines library."
Revert "Do not use a global variable in coroutines library."

This reverts commit fa0ca9c95502385b1797ed2d3c0e9a973ad2c62c.

The fix is not complete for 32 bits machines. Will work on a
correct fix later.

aldebaran/libport,aldebaran/libport,aldebaran/libport,aldebaran/libport,aldebaran/libport