MFH: r405494

security/nss: update to 3.21

Temporarily disable gtests as they require C++0x support and install a
library that may have conflicting API with devel/googletest.

Changes: https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/NSS_3.21_release_notes
Approved by: ports-secteam (feld)