[CMake] missing INTERFACE_LINK_LIBRARIES in target export files

[Nico Schlömer]

Hi all,

in a CMake project of mine, I build shared libraries and link against
third-party shared libraries. In the export target files, I find
```
add_library(mylib SHARED IMPORTED)
```
as expected, but I'm *missing* anything along the lines of
```
set_target_properties(mylib PROPERTIES
  INTERFACE_INCLUDE_DIRECTORIES "${_IMPORT_PREFIX}/include"
  INTERFACE_LINK_LIBRARIES "/usr/lib/lapack.so"
)
```
Any idea why this isn't present? Note that I'm *not* using the
`PRIVATE` keyword in `TARGET_LINK_LIBRARIES()`.

Cheers,
Nico