Support for setting per-file host copt (e.g. --host_per_file_copt)

[GMNGeoffrey]

Description of the problem / feature request:

Ability to set host only per-file copt. Basically the combination of per_file_copt and host_copt

Feature requests: what underlying problem are you trying to solve with this feature?

Our repository depends on other repositories. We use per_file_copt to turn of clang diagnostics for these other repositories and then set -Werror, but this doesn't work in host mode because there's no way to do things per-file.

What operating system are you running Bazel on?

Linux Debian

What's the output of bazel info release?

release 3.3.1

What's the output of git remote get-url origin ; git rev-parse main ; git rev-parse HEAD ?

$ git remote get-url origin ; git rev-parse main ; git rev-parse HEAD
git@github.com:GMNGeoffrey/iree.git
d13da6a832c3b75ea58129cff1936d39d2005610
361087f36af996632800d1bf9c4bdfa754a645ba

Have you found anything relevant by searching the web?

No

[GMNGeoffrey]

Just for future people who are perhaps interested in this feature for the same reason, we ended up just turning off all host build diagnostics. We build everything we care about as a target as well, so we'll see the diagnostics there.

https://github.com/google/iree/blob/a15d08f3adba62b9541824fc55e5501711da08f5/build_tools/bazel/iree.bazelrc#L84

[keith]

#16618

[UebelAndre]

I've opened a cherry-pick for the 6.0 release per the guidance here: #16159 (comment)

• Add --host_per_file_copt #16695