cmake-build-system: build tests only if #:tests? is true?

[Hartmut Goebel]

Hi,

I found an old and unfinished patch in my pile. It optimizes building 
with cmake by not building the test if "#:tests?" is false. (Basically 
it passes -DBUILD_TESTING=OFF/ON" depending on "#:tests?".)

Is this of interest? Then I would take my time and finish the patch.

--
Regards
Hartmut Goebel

| Hartmut Goebel          | h.goebel@crazy-compilers.com               |
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