Simplify TmpIndexNode memsector export.

Summary:
 - Fix memsector export on Mac OSX.
 - Simplify TmpIndexNode code path.
 - Change default build type to debug.

Test Plan: > make test

Reviewers: radu.hambasan, dhasegan

Reviewed By: radu.hambasan

Differential Revision: http://phab.code4fun.de/D41