CMake: Use LAPACK imported target

[gardner48]

1. Use LAPACK::LAPACK rather than LAPACK_LIBRARIES
2. Simplify try_compile test
3. Don't overwrite LAPACK_WORKS (test every configuration pass)
4. Use CHECK_START, CHECK_PASSED, and CHECK_FAILED messages in compile test
5. Replace manual include guard with include_guard(GLOBAL)
6. Update SundialsTPL.cmake.template with above changes

[gardner48]

This may help address #350.

[gardner48]

@balos1 If you're good with the updates to SundialsTPL.cmake.template and LAPACK_WORKS, I'll see about propagating these changes to the other TPL files (in follow on PRs).

With LAPACK_WORKS this is now only used to bypass the compile test and not to indicate if the compile test passed (since failing is a fatal error). So _WORKS might not be the best name, maybe LAPACK_TEST or SUNDIALS_LAPACK_TEST or SUN_LAPACK_TEST (for better namespacing).

[balos1]

This looks great!

[gardner48]

Looks like there is a problem with the compile test that might be specific to CMake 3.18, I'm looking into it.

[Steven-Roberts]

This fixes the missing linking flags issue I had. When I have two lapack versions (system and spack) it finds both in cmake and only uses the system version for compilation. It's unclear how I would use the spack version for compilation.

[gardner48]

It's unclear how I would use the spack version for compilation.

Unfortunately FindLAPACK does not seem to support the usual _ROOT or _DIR options to help the set search path so you'll probably have to set LAPACK_LIBRARIES and LAPACK_LINKER_FLAGS manually. I've not tried it but setting BLA_VENDOR might also work e.g., -DBLA_VENDOR="OpenBLAS"

[Steven-Roberts]

Got it working with David's help. For posterity, -DBLA_VENDOR="OpenBLAS" did work as well as manually setting LAPACK_LIBRARIES and LAPACK_LINKER_FLAGS. Just had to make sure the compiler version was consistent with the OpenBLAS build from spack.

[Steven-Roberts]

@gardner48 The latest version still works for me, both with a system LAPACK and spack one.