Bug 959356 - Report isWow64 in Firefox Health Report; r=bsmedberg

Previously, we weren't measuring whether the machine was 64-bit
properly. This change allows us to report actual CPU architecture (at
least on Windows).

In the future, we may wish to properly report actual CPU architecture on
all operating systems.

--HG--
extra : rebase_source : 73b5673e870e959a33172ec22fee8c31db6e0e53
extra : amend_source : 64d2e23be07aa87bc5c150b6e613e6226c848ec8