Support for per-file flags

[flit]

Some projects require per-file compiler flags.

This should probably work by allowing a source file entry to be a usual settings dict.

[0xc0170]

I recall working on some projects that had specific files settings. I always wanted to avoid this (it is hidden from common settings).

The support for all tools will take the most effort.

[flit]

Yeah, it's a pain. Unfortunately it's needed for some things I'm working on in Research. Currently I'm working around it with a new tool-specific custom_rules setting added in my fork. It accepts a string that is just copied directly into the generated Makefile or CMakeLists.txt.

[eleenest]

Just curious if this feature is still in the works.

Not urgent, but we did have a case where we wanted to apply flags to only some files (i.e. enable -Werror for files that have been cleaned up, so they stay clean).

Eric