external/boringssl: add -Wno-unused-parameters.

Clang is throwing errors becaues of unused parameters, but not all
parameters are supposed to be used. Also, having errors in Android that
aren't enforced upstream invites this problem repeating ever more in the
future.

Bug: 21304073
Change-Id: I8e81d6d6659896b5b16a1406e8637e489f8059fd
1 file changed