Fix -Wshadow for tools

Summary: Previously I made `make check` work with -Wshadow, but there are some tools that are not compiled using `make check`.

Test Plan: make all

Reviewers: yhchiang, rven, ljin, sdong

Reviewed By: ljin, sdong

Subscribers: dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D28497