Simd generates many test sources during cmake configuration

In dune/common/simd/test a lot of files are generated during the CMake configuration run. As far as I understand, it is related to the problem that one big test would need too much memory. Thus, it is split up into smaller tests. See #151 (closed), !633 (merged), and !193 (merged). So, this file generation for the simd tests probably makes perfectly sense.

But, I see 100s of lines of output during the standard cmake configuration. This makes it harder to find actual problems in cmake and to inspect the output for missing files.

• Is it necessary to see all the files that are generated for the tests? (Maybe we can turn the message(STATUS "Generating A -> B") into a log message in CMakeOutput.txt instead of printing it always)
• Wouldn't it be better to generate the files only when requesting to build the simd tests? Or even make it part of the test? (Maybe this can be achieved by writing a custom target or run a cmake script on build of the tests)