libstdc++: Abort test after 1000 lines of output

libstdc++: Abort test after 1000 lines of output

Handle overly large output by aborting the log and thus the test. This
is a similar condition to a timeout.

libstdc++-v3/ChangeLog:

	* testsuite/experimental/simd/driver.sh: When handling the pipe
	to log (and on verbose to stdout) count the lines. If it exceeds
	1000 log the issue and exit 125, which is then handled as a
	failure.