[Sanitizer] Add Symbolizer::AddHooks() and use it in TSan and MSan.

Summary:
TSan and MSan need to know if interceptor was called by the
user code or by the symbolizer and use pre- and post-symbolization hooks
for that. Make Symbolizer class responsible for calling these hooks instead.
This would ensure the hooks are only called when necessary (during
in-process symbolization, they are not needed for out-of-process) and
save specific sanitizers from tracing all places in the code where symbolization
will be performed.

Reviewers: eugenis, dvyukov

Reviewed By: eugenis

CC: llvm-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D2067