Summary:
This mirrors what we use when building thrift.
Without this, boost somehow picks a mix of static and shared
libs, but the static linkage doesn't know how to find the libdir
and thus the link fails.

This bubbles up when building folly's tests, which also require
linking with glog.

Reviewed By: yfeldblum

Differential Revision: D14700315

fbshipit-source-id: a331fdb493e7af62b42833b90bd20367778642ea