bpo-32890, os: Use errno instead of GetLastError() in execve() and truncate() (GH...

bpo-32890, os: Use errno instead of GetLastError() in execve() and truncate() (GH-5784)

path_error() uses GetLastError() on Windows, but some os functions
are implemented via CRT APIs which report errors via errno.
This may result in raising OSError with invalid error code (such
as zero).

Introduce posix_path_error() function and use it where appropriate.
(cherry picked from commit 834603112e6ca35944dd21105b01fca562dc3241)

Co-authored-by: Alexey Izbyshev <izbyshev@ispras.ru>