[CMake] Fix lld detection after D69685

D69685 actually broke lld detection for my build (probably due to CMake
processing order).

Before:

```
build projects/compiler-rt/lib/sanitizer_common/tests/Sanitizer-x86_64-Test-Nolibc: ... bin/clang || ...
```

After:

```
build projects/compiler-rt/lib/sanitizer_common/tests/Sanitizer-x86_64-Test-Nolibc: ... bin/clang bin/lld || ...
```

Differential Revision: https://reviews.llvm.org/D71950