This patch allows usage of multilib.yaml when using a riscv gnu toolchain
This could certainly land as three separate patches, but I wanted to put this up as one to gather feedback to make sure the direction makes sense.
These are the main discussion points I want to bring to attention:
- For the RISCVMultilibFlags, the mabi flag is used in combination with all the march extension features (e.g +m). Notably, this doesn't align with the current arm/aarch64 multilib flags, which all flags corresponding to the command line flag. E.G -march=. Does this violate a particular design decision, or can any target decide on whatever multilib flags they want?
- The location of multilib.yaml for a gnu toolchain is in the lib directory of the sysroot. E.G riscv64-unknown-elf/lib/multilib.yaml. This differs from the baremetal location of "lib/clang-runtimes".
- Does it make more sense to implement finding multilibs using yaml for riscv in the baremetal toolchain first? I was planning on doing it after.
Theoretically, I think this matching of multilibs could be done without the need for multilib.yaml, but it is indeed much easier considering the logic is already there.