Veclib flags not being passed to LTO flags

[paschalis-mpeis]

We want to backport PR #78749 so the release has this feature.

The above PR converts clang's -fveclib flag to their equivalent name for opt's -vector-library,
so they are propagated correctly when LTO is used.

[llvmbot]

@llvm/issue-subscribers-clang-driver

Author: Paschalis Mpeis (paschalis-mpeis)

We want to backport PR #78749 so the release has this feature.

The above PR converts clang's -fveclib flag to their equivalent name for opt's -vector-library,
so they are propagated correctly when LTO is used.

[github-actions]

/pull-request #79566

[tstellar]

Merged: fa0a72b