[clang] [Multilib] Custom flags YAML parsing (PR #110657)

[Peter Smith via cfe-commits]

smithp35 wrote:

> This patch adds support for custom flags in the multilib YAML file.
> 
> Details about this change can be found in this thread: https://discourse.llvm.org/t/rfc-multilib-custom-flags/81058

Apologies in advance for being a pain. Prior to commit, assuming that the RFC has stabilised, please could the description be updated to give a summary of custom flags and what this part of the patch adds. It is fine to link to the RFC, although that may not be as permanent as we'd like and it makes it harder for someone searching for the commit log to find the patch.



https://github.com/llvm/llvm-project/pull/110657