stdio-common: Add test for vfscanf with matches longer than INT_MAX [BZ #27650]

stdio-common: Add test for vfscanf with matches longer than INT_MAX [BZ #27650]

Complement commit b03e4d7bd25b ("stdio: fix vfscanf with matches longer
than INT_MAX (bug 27650)") and add a test case for the issue, inspired
by the reproducer provided with the bug report.

This has been verified to succeed as from the commit referred and fail
beforehand.

As the test requires 2GiB of data to be passed around its performance
has been evaluated using a choice of systems and the execution time
determined to be respectively in the range of 9s for POWER9@2.166GHz,
24s for FU740@1.2GHz, and 40s for 74Kf@950MHz.  As this is on the verge
of and beyond the default timeout it has been increased by the factor of
8.  Regardless, following recent practice the test has been added to the
standard rather than extended set.

Reviewed-by: DJ Delorie <dj@redhat.com>