MB-8804: Add visibility tags

Change-Id: I3779017e5752a8735ada758620669419214b3b7b
MB-8804: Remove unused method

Change-Id: I8d142fe8e9fb7173730d2d7c7d48fd9e1f168bc4
MB-8804: Don't check for unused header files

Change-Id: I1484b3bf7074b00917e7db7287fdb913c4503d6b
MB-8804: Don't check for "standard" headerfiles

There is no point of search for header files listed in the
language spec (like stdlib.h etc)

Change-Id: I2e2512f3e16ed57245f43866fd80e2ed6b420fff
MB-8804: Don't expose the inner workings of the SASL library

The clients shouldn't touch the internals of the library
and shouldn't know what it looks like.

Change-Id: I34c3db8683b5b220275f48086bd02c70fb3c91b3