[llvm] [CMake] Support per-target linker flags (PR #68393)

[Vincent Lee via llvm-commits]

thevinster wrote:

> The alternatives I could think of is setting the linker flags at the per-distribution granularity.

For us, we define a set of distribution as well for other teams to use. But even with our filtered down distribution, we'd still like to only apply `-Wl,--lto-O0` since tools like `llvm-objdump` or `llvm-nm` are necessary for integration with our build system for debugging, but not necessary to be LTO-ed since they aren't in the critical path of release builds. 

https://github.com/llvm/llvm-project/pull/68393