FindCUDA: Always list custom command outputs in their targets

CMake's intended interface for linking to explicit object files (marked
with EXTERNAL_OBJECT) is that only those listed as target sources should
be linked.  Drop FindCUDA's attempt to hide the .obj files from VS IDE
project files, which depends on VS-version-specific behavior of linking
custom command outputs that happen to be named "*.obj".  CMake puts
external object files in a dedicated source group anyway.
genex: Fix preprocessing with incomplete content (#14410).

Similar incomplete generator expressions are already tested
in the GeneratorExpression unit test, but those are executed
with add_custom_target. The generator expressions in the include
directories are run through the preprocessor, whereas the ones
run through add_custom_target are not.
Merge topic 'fix-genex-preprocessing-incomplete'

70089d0 genex: Fix preprocessing with incomplete content (#14410).
Merge topic 'FindCUDA-list-obj-files'

ef27fa6 FindCUDA: Always list custom command outputs in their targets