ovs-dev.py: Support additional optimization flags.

They may or may not make a difference, but there's no reason not to
support passing them.

Signed-off-by: Ethan Jackson <ethan@nicira.com>
Acked-by: Daniele Di Proietto <ddiproietto@vmware.com>
ovs-dev.py: Support running the clang binaries.

They have slightly different support characteristics, so it's nice to
easily switch between them for testing.

Signed-off-by: Ethan Jackson <ethan@nicira.com>
Acked-by: Daniele Di Proietto <ddiproietto@vmware.com>