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

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `clang-arm64-windows-msvc` running on `linaro-armv8-windows-msvc-04` while building `lld` at step 5 "ninja check 1".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/161/builds/2583

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 5 (ninja check 1) failure: 1200 seconds without output running [b'ninja', b'check-all'], attempting to kill
******************** TEST 'lld :: ELF/aarch64-thunk-bti.s' FAILED ********************
Exit Code: 1

Command Output (stdout):
--
# RUN: at line 2
rm -rf C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\lld\test\ELF\Output\aarch64-thunk-bti.s.tmp && split-file C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\lld\test\ELF\Output\aarch64-thunk-bti.s.tmp && cd C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\lld\test\ELF\Output\aarch64-thunk-bti.s.tmp
# executed command: rm -rf 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\lld\test\ELF\Output\aarch64-thunk-bti.s.tmp'
# executed command: split-file 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s' 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\lld\test\ELF\Output\aarch64-thunk-bti.s.tmp'
# executed command: cd 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\tools\lld\test\ELF\Output\aarch64-thunk-bti.s.tmp'
# RUN: at line 3
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-mc.exe -filetype=obj -triple=aarch64 asm -o a.o
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-mc.exe' -filetype=obj -triple=aarch64 asm -o a.o
# RUN: at line 4
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\ld.lld.exe --threads=1 --shared --script=lds a.o -o out.so --defsym absolute=0xf0000000
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\ld.lld.exe' --threads=1 --shared --script=lds a.o -o out.so --defsym absolute=0xf0000000
# RUN: at line 5
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-objdump.exe -d --no-show-raw-insn out.so | c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\filecheck.exe C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-objdump.exe' -d --no-show-raw-insn out.so
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\filecheck.exe' 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s'
# RUN: at line 6
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-objdump.exe -d --no-show-raw-insn out.so | c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\filecheck.exe C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s --check-prefix=CHECK-PADS
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-objdump.exe' -d --no-show-raw-insn out.so
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\filecheck.exe' 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s' --check-prefix=CHECK-PADS
# RUN: at line 7
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-mc.exe -filetype=obj -triple=aarch64 shared -o shared.o
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-mc.exe' -filetype=obj -triple=aarch64 shared -o shared.o
# RUN: at line 8
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\ld.lld.exe --shared -o shared.so shared.o
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\ld.lld.exe' --shared -o shared.so shared.o
# RUN: at line 9
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\ld.lld.exe shared.so --script=lds a.o -o exe --defsym absolute=0xf0000000
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\ld.lld.exe' shared.so --script=lds a.o -o exe --defsym absolute=0xf0000000
# RUN: at line 10
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-objdump.exe -d --no-show-raw-insn exe | c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\filecheck.exe C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s --check-prefix=CHECK-EXE
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-objdump.exe' -d --no-show-raw-insn exe
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\filecheck.exe' 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s' --check-prefix=CHECK-EXE
# RUN: at line 11
c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-objdump.exe -d --no-show-raw-insn exe | c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\filecheck.exe C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s --check-prefix=CHECK-PADS
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\llvm-objdump.exe' -d --no-show-raw-insn exe
# executed command: 'c:\users\tcwg\llvm-worker\clang-arm64-windows-msvc\stage1\bin\filecheck.exe' 'C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s' --check-prefix=CHECK-PADS
# .---command stderr------------
# | C:\Users\tcwg\llvm-worker\clang-arm64-windows-msvc\llvm\lld\test\ELF\aarch64-thunk-bti.s:250:21: error: CHECK-PADS-NEXT: expected string not found in input
# | // CHECK-PADS-NEXT: udf #0x0
# |                     ^
# | <stdin>:103:29: note: scanning from here
# | 18001048: b 0x18001050 <fn4>
# |                             ^
# | <stdin>:106:1: note: possible intended match here
# | 0000000018001050 <fn4>:
...

```

</details>

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