This flag is on by default for darwin and freebsd, but off for linux.
Without it, clang will sometimes not emit debug info for types like
std::string. Whether it does this, and which tests will fail because of
that depends on the linux distro and c++ library version.
A bunch of tests were already setting these flags manually, but here
instead I take a whole sale approach and enable this flag for all tests.
Any test which does not want to have this flag (right now we have one
such test) can turn it off explicitly via
Can you check whether this makes any difference for test results on