Allow linking against build tree

[masterleinad]

This pull request makes it possible to link against Kokkos using the build tree which is, e.g., very useful when trying out how changes in Kokkos influence downstream code (and having changes ready to create pull requests).

This is necessary for trilinos/Trilinos#11779.

[bartlettroscoe]

The only thing that may be needed for building Kokkos inside of Trilinos with the native Kokkos CMake build system is the location of the KokkosConfig.cmake file for the build tree. TriBITS assumes these files are stored under <buildDir>/cmake_packages/<Package>/<Package>Config.cmake (see 4.1 TriBITS-Compliant Internal Packages and 8.7 Using packages from the build tree in downstream CMake projects).

Hopefully this is a simple tweak to the Kokkos CMake files to be able to specify the exact location of where to put this KokkosConfig.cmake file for the build tree.

[masterleinad]

The only thing that may be needed for building Kokkos inside of Trilinos with the native Kokkos CMake build system is the location of the KokkosConfig.cmake file for the build tree. TriBITS assumes these files are stored under <buildDir>/cmake_packages/<Package>/<Package>Config.cmake (see 4.1 TriBITS-Compliant Internal Packages and 8.7 Using packages from the build tree in downstream CMake projects).

It seems that trilinos/Trilinos#11779 also works with these files in

<buildDir>/packages/kokkos/

[bartlettroscoe]

It seems that trilinos/Trilinos#11779 also works with these files in

<buildDir>/packages/kokkos/

@masterleinad, the standard build and install of Trilinos packages do not utilize the files under <buildDir>/cmake_packages/. Instead, these are utilized by downstream customers that don't want to install the packages to be able to use the built libraries, etc. (See 8.7 Using packages from the build tree in downstream CMake projects).

I will add a test to the TrilinosInstallTests package to demonstrate and protect this functionality.

Also, these files are utilized for incremental configures and builds as described in Use Case 1: Configure/build all packages then re-configure subset of downstream packages as part of:

• EPIC: Merge TriBITS concepts and implementation of Packages and TPLs TriBITSPub/TriBITS#63

I have not added the official documentation for this use case to TriBITS yet, but this use case will speed up re-configures/re-builds for developers that have a local build and just want to reconfigure/rebuild a small subset of downstream packages. (For a small TriBITS project like Trilinos this is not that big of a deal but for larger TriBITS projects like CASL VERA, this will have greater impact on reducing reconfigure times and build-time dependency computation.)

[dalg24]

HIP builds timed out but that's ok