libstdc++: Improve output verbosity options and default

libstdc++: Improve output verbosity options and default

For most uses --quiet was too quiet while the default was too noisy. Now
the default output, if stdout is a tty, shows the last successful test
on the same line. With --percentage it adds a percentage at the start of
the line. --percentage is not default because it requires more resources
and might not be 100% compatible to all environments.
If stdout is not a tty the default is quiet output like for dejagnu.

Additionally, argument parsing now recognizes contracted short options
which is easier to use with e.g. DRIVEROPTS=-pxk.

Signed-off-by: Matthias Kretz <m.kretz@gsi.de>
libstdc++-v3/ChangeLog:

	* testsuite/experimental/simd/driver.sh: Rewrite output
	verbosity logic. Add -p/--percentage option. Allow -v/--verbose
	to be used twice. Add -x and -o short options. Parse long
	options with = instead of separating space generically. Parce
	contracted short options. Make unrecognized options an error.
	If same-line output is active, trap on EXIT to increment the
	progress (only with --percentage), erase the line and print the
	current status.
	* testsuite/experimental/simd/generate_makefile.sh: Initialize
	helper files for progress account keeping. Update help target
	for changes to DRIVEROPTS.