[Unit tests] skip BLAS and LAPACK unit tests if Netlib is not found

[mkrainiuk]

Description

This PR implements one more possible solution for the problem described in #557
In case Netlib libraries are not available it shouldn't block completely oneMKL Interfaces building, instead we can generate warning that BLAS and LAPACK unit tests will be skipped because of Netlib absence.

This PR also includes some pre-work for adding BLAS and LAPACK tests that won't require Netlib.

• Example of the output users will get if Netlib is found

-- Found LAPACKE: /usr/lib64/liblapacke64.so
-- Found LAPACKE: /usr/lib64/liblapack64.so
-- Found LAPACKE: /usr/lib64/libcblas64.so
-- Found LAPACKE: /usr/lib64/libblas64.so
-- Found LAPACKE: /usr/include
...
-- Configuring done
-- Generating done

• Example of the output users will get if Netlib is NOT found

-- Could NOT find LAPACKE (missing: LAPACKE64_file)
-- Could NOT find LAPACKE (missing: LAPACK64_file)
-- Could NOT find LAPACKE (missing: CBLAS64_file)
-- Could NOT find LAPACKE (missing: BLAS64_file)
-- Could NOT find LAPACKE (missing: LAPACKE_INCLUDE LAPACKE_LINK)
CMake Warning at tests/unit_tests/CMakeLists.txt:33 (message):
  Netlib LAPACKE headers or libraries are not found, LAPACK unit tests will
  be skipped
...
-- Configuring done
-- Generating done

Checklist

All Submissions

• Do all unit tests pass locally? Attach a log. Both public and internal CIs were passed
• Have you formatted the code using clang-format? N/A, all changes are CMake related only

[Rbiessy]

LGTM!

[andrewtbarker]

Look good, thanks for the changes!

[andrewtbarker]

I don't really follow this syntax, but are we changing this argument from PUBLIC to non-public?

[mkrainiuk]

New logic helps us to drop CBLAS_INCLUDE from the compilation line when CBLAS header file is not found. Otherwise it might appear in the compilation line as -ICBLAS_INCLUDE_not_found and cause test compilation issue.

As for PUBLIC keyword since each BLAS test is a final binary, not library, we don't need to mark this dependency as needed to be propagated to other targets that depend on this target, because we don't have such targets.