Refactor loader specific CMake options

Refactor loader specific CMake options

Create a new target loader_specific_options that contains the specific flags
and definitions which apply only to the loader. This target links to the
loader_common_options and is used to store various macro defines which
only are relevant to the loader, like the specific language standard to use.
The target also links to the vulkan headers.
Note that this commit is in a series of commits and is not meant to work
by itself.