libstdc++: Immediate feedback with -v

libstdc++: Immediate feedback with -v

libstdc++-v3/ChangeLog:

	* testsuite/experimental/simd/driver.sh: Remove executable on
	SIGINT. Process compiler and test executable output: In verbose
	mode print messages immediately, limited to 1000 lines and
	breaking long lines to below $COLUMNS (or 1024 if not set).
	Communicating the exit status of the compiler / test with the
	necessary pipe is done via a message through stdout/-in.