According to the ISO/IEC_9899_1999, section: J.5.16 it is mentioned that there is a file position indicator that is decremented by each call of the ungetc function.

The value of the file position indicator was not directed to the right position, this issue is now handled in the ftell function
so the file indicator is placed correctly after the function
ungetc is called.
An "if" condition is added which checks on the value of unget and if it is not equal zero then ungetc function is called so the indicator will be decremented.

Signed-off-by: Hana Ashour <[email protected]>

This allows fetching the unget value using stdatomic interfaces to
ensure atomicity wrt other unget operations.

Signed-off-by: Keith Packard <[email protected]>

A pending unget value means that the underlying reported seek position
will be off by one.

Signed-off-by: Keith Packard <[email protected]>

Make sure ungetc affects ftell value correctly.

Signed-off-by: Keith Packard <[email protected]>

pulled the changes from PR picolibc#719 and changed the copyrights in the test

Signed-off-by: Hana Ashour <[email protected]>