[lld] [ELF] Change Ctx::target to unique_ptr (PR #111260)

[via llvm-commits]

zeroomega wrote:

> > We also see a weird issue on Windows is that during clang test step, lld timed out: `Linking CXX executable unittests\Transforms\Scalar\ScalarTests.exe` took 36 minutes and caused the bot timed out. Your change is the only on the blamelist.
> 
> @zeroomega is this repeatable? We haven't seen this on our windows builds.
> 
> EDIT - we're not seeing any timeouts.. but I will check for excessive test times.

So I did a few test runs locally.

The test timeout (I should say lit probably hanged) on test `ELF/aarch64-cortex-a53-843419-thunk-align.s`
If I run `ninja check-lld` with "-DLLVM_LIT_ARGS=-v -j64" , I have a high chance that the `check-lld` will hang. The host machine is a 16 cores 32 threads machine. However, if I reduces the -j to 16 or even 1, the test will finish with error on `lld :: ELF/aarch64-thunk-bti.s`.  Comparing finished test run with the one that hang, I discovered that `ELF/aarch64-cortex-a53-843419-thunk-align.s` was not on the list of finished test when `-j64` was used.  The hang issue resolved itself after this patch was reverted. Could it be some deadlock issue introduced to lld in this patch?

https://github.com/llvm/llvm-project/pull/111260