Fix fetch method causing test-drive tests to be included in CTest list

[topherocity]

Good evening folks,

Thanks for all the work you are doing to reviving Fortran into a more modern language!

I'm attempting to add some unit testing to a rather old Fortran code base using CMake, and followed the steps shown in this repository for integrating test-drive into my project. However, I noticed rather quickly that the tests from test-drive were making it into my own project testing and failing:

$ make all test
...
25% tests passed, 3 tests failed out of 4

Total Test time (real) =   0.01 sec

The following tests FAILED:
          2 - test-drive/all-tests (Not Run)
          3 - test-drive/check (Not Run)
          4 - test-drive/select (Not Run)

I don't think this happens on the cmake and pkgconf methods in Findtest-drive.cmake, because both of those are installed paths with no mention of tests.

This pull request fixes this by defining a TEST_DRIVE_BUILD_TESTING option that will not be defined if test-drive is linked to after FetchContent.

[codecov]

Codecov Report

Merging #18 (58143b3) into main (a1ab785) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main      #18   +/-   ##
=======================================
  Coverage   71.51%   71.51%           
=======================================
  Files           2        2           
  Lines         481      481           
  Branches      296      296           
=======================================
  Hits          344      344           
  Misses         23       23           
  Partials      114      114           

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[awvwgk]

Thanks for sharing. Added a minor change to also include BUILD_TESTING

[certik]

@topherocity Thanks for the PR! If you have more improvements, definitely let us know.