CMake: Fix export with AMReX_INSTALL=OFF

[ax3l]

Summary

When introducing AMReX_INSTALL #1831, the export of targets #1149 broke for OFF. This generalizes this to work in either case.

Additional background

Check the change without white space changes to see the changed logic more cleanly:
https://github.com/AMReX-Codes/amrex/pull/2838/files?diff=unified&w=1

Checklist

The proposed changes:

• fix a bug or incorrect behavior in AMReX
• add new capabilities to AMReX
• changes answers in the test suite to more than roundoff level
• are likely to significantly affect the results of downstream AMReX users
• include documentation in the code and/or rst files, if appropriate

[ax3l]

This line only works if an equivalent install() line exists for the same target.

[ax3l]

@jmusser304 let's coordinate here on your regression in MFIX

Quote:
MFIX complains about CUDA::curand not found

CMake Error at subprojects/amrex/builddir/lib/cmake/AMReX/AMReXTargets.cmake:51 (set_target_properties):
  The link interface of target "AMReX::amrex" contains:

    CUDA::curand

if I run the same command echoed by the regtest, it works
oddly, MFIX link line reported by cmake from regtest contains curand

--    MFIX link line        = -pthread /.nfs/misc/apps/MPI/openmpi/4.0.4/gnu/9.3.0/cuda/10.2/lib/libmpi.so CUDA::curand /nfs/apps/Compilers/NVIDIA/CUDA/11.3/targets/x86_64-linux/lib/stubs/libcurand.so 

[jmusser304]

It appears that I can get it to build if edit the file <path to amrex builddir>/lib/cmake/AMReX/AMReXTargets.cmake and remove the CUDA::curand from the line

INTERFACE_LINK_LIBRARIES "Threads::Threads;MPI::MPI_C;MPI::MPI_CXX;CUDA::curand;AMReX::Flags_CXX"

[ax3l]

Fixed via #2849