[cmake] Properly support target properties.

It's sometimes useful to use these directives when dealing with
external projects:
target_link_directories
target_link_libraries
target_include_directories

However, under certain circumstances,
llvm_add_library can generate multiple targets.  We need to transfer
these properties to the new targets.  Note that using a generator
expression is necessary because these properties will only be set
after llvm_add_library is called.

Differential Revision: https://reviews.llvm.org/D108098