Add mold preloading support

mold is a new linker, replacing ld, gold, or lld and it is amazingly fast. From their issue tracker, there is a feature request (#74) that actually belongs here:

mold supports object file preloading feature. In order to use it, someone has to run a linker command with --preload flag a few seconds prior to the actual linker invocation. And I think "someone" should be a build system, such as make or ninja executing CMake-generated ninja or Makefiles.

As a starter, I think we should add the following feature to CMake:

Detect if a linker is mold

run a linker command with --preload if it is mold before invoking compiler instances to generate object files

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information