Add support for include-what-you-use

[gewenyu99]

Originally by Tyler Jang, moved from Canny

Trunk already has support for IWYU, but it lacks feature-completeness when reading from compile_commands.json, resulting in an error like:
error: no such file or directory: '../main.cpp'
error: no input files
error: unable to handle compilation, expected exactly one compiler job in ''
We should fully support this use case.