Revert "SERVER-12272 Suppress new GCC 4.8 warning about unused local typedefs"

This reverts commit 7fa028e8fa7b961d69769172565791b1dd5caec4.

Older GCC doesn't silently ignore attempts to disable warnings it doesn't
know about, so -Wno-unused-local-typedefs breaks the build.
Merge remote-tracking branch 'upstream/v2.4' into v2.4