Investigate: Clean way of marking small subset of files to compile as debug in release build

I've had two teams have a bug only show up in a release build and wanted a non-gross way of flagging a very small subset of files to compile as debug. Is this possible without hacking the compile flags on those files directly in the build system? Can BLT clean this up?

Start by reviewing BLT's CMake-based build-system configuration and how it handles compile flags for release builds. Determine whether a supported mechanism can mark a small subset of files for debug compilation without direct per-file flag edits; done means the supported approach and its limits are clearly established.

Written by the indexing model from the issue text.