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

[Peter Smith via llvm-commits]

smithp35 wrote:

FWIW the sanitizer test failure can be fixed by initialising trapInstr
```
diff --git a/lld/ELF/Arch/AArch64.cpp b/lld/ELF/Arch/AArch64.cpp
index 1368e209c8cf..e67366584b97 100644
--- a/lld/ELF/Arch/AArch64.cpp
+++ b/lld/ELF/Arch/AArch64.cpp
@@ -126,7 +126,7 @@ AArch64::AArch64(Ctx &ctx) : TargetInfo(ctx) {
   // Align to the 2 MiB page size (known as a superpage or huge page).
   // FreeBSD automatically promotes 2 MiB-aligned allocations.
   defaultImageBase = 0x200000;
-
+  trapInstr = {0x0, 0x0, 0x0, 0x0};
   needsThunks = true;
 }
```

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