Errors printed using OS_printf may never appear

[jphickey]

Describe the bug
OS_printf uses an additional output buffer with a low priority task to move the data from the buffer to the console. In the case of fatal errors which cause the process to exit as a result, the output may not get transferred before the process exits and the task is killed.

To Reproduce
See #202 of a case where (for other reasons) shmget failed but no error message was shown.

Expected behavior
Error messages should be shown

Additional context
This is particularly an issue for errors which cause an immediate process exit. So long as the process keeps running and the output task isn't immediately cancelled, there should not be an issue.

Recommendation is to use fprintf(stderr, ...) for fatal error messages, as even the stdout stream might have some line buffering in the C library, but the stderr stream should be (relatively) unbuffered.

Reporter Info
Joseph Hickey, Vantage Systems, Inc. ( based on previous report in #202 )