e10s profiling or IR-based PGO instrumentation will both produce
multiple `.profraw` files that need to be handled in some way. Since
clang's `-fprofile-generate` option takes a directory, it seems fitting
to make `--with-pgo-profile-path` mirror that by taking a directory, and
letting `merge_profdata.py` deal with whatever files it might find in
said directory.
Differential Revision: https://phabricator.services.mozilla.com/D32389
--HG--
extra : moz-landing-system : lando
