Support emulation options when invoking ld.eld directly.

[Kali (EagleEye-0101)]

Summary

• Extend ld.eld driver selection to honor -march variants, -mtriple, and -mcpu without requiring target-specific symlink names (arm-link, riscv-link, etc.)
• Detect and reject conflicting target options across emulation flags
• Tighten ARM -m emulation validation to match supported emulation strings
• Add LIT coverage for ld.eld-only invocation paths and re-enable Hexagon invalid-emulation checks

Closes #21. Builds on prior work in #22/#23 and #54/#55.

Test plan

• qualcomm CI (ci.yml) passes — ninja check-eld
• Clang format check passes
• QC preflight checks pass
• New tests under test/Common/standalone/EmulationOptions/ and test/*/standalone/EmulationOptions/
• Re-enabled test/Hexagon/standalone/InvalidEmulation/InvalidEmulation.test

[Kali (EagleEye-0101)]

Hi, I'm working on #21 by extending ld.eld driver selection for -march/-mtriple/-mcpu
(without needing arm-link etc.), I added some LIT tests as well.

Happy to make any changes based on your feedback.
Please review and approve, hoping to hear soon.

[Shankar Easwaran (quic-seaswara)]

added a comment in the issue

[Kali (EagleEye-0101)]

Hi Shankar Easwaran (@quic-seaswara), thanks for the comment on issue #21, I read it and pushed an update.

I removed using -march and -mtriple for ld.eld driver selection, since those aren't standard for the generic linker name. The PR now focuses on -m emulation (including tighter ARM validation and Template support from main), -mcpu where it helps pick the driver (e.g. Hexagon), and rejecting conflicting target options.

Please let me know if -mcpu should be removed from ld.eld driver selection as well, or if anything else should change. Happy to adjust.