[compiler-rt] Check if LLD is built when checking if lto_supported (PR #92752)

[Jan Voung via llvm-commits]

jvoung wrote:

Thanks!
I compared the number of tests on build before and after in the sanitizer bots: https://docs.google.com/spreadsheets/d/1STjhM3EFr3YldkpCN40Lic2Qk2Ga2uBoqINYub5Fjxs/edit?usp=sharing

overall they look same except one case `stage2/ubsan check-cxx` on bot [sanitizer-x86_64-linux-bootstrap-ubsan](https://lab.llvm.org/buildbot/#/builders/85).
- There the number of excluded, unsupported, skip, etc. are the same
- Only the number of "passed" / total tests is fewer. I believe that's because the run batched this commit with [another commit](https://github.com/llvm/llvm-project/commit/716ed5fccd2a960981fec2c5acb17292a1502435) that reverted/deleted some libcxx tests.

https://github.com/llvm/llvm-project/pull/92752