HHVM itself does not depend on boost_regex.
Only third-party/folly depends on libboost_regex, but HHVM has a
dependency that causes a bogus linkage in the final binary.

Sync with Debian patch 09_remove_boost_regex_hhvm.patch from 2.4.1-1.
Merge pull request #2086 from Jo-Con-El/debian-09_remove_boost_regex_hhvm

HHVM itself does not depend on boost_regex.