Buggy CMake config

[chrisosaurus]

Running CMake once or twice with the COVERAGE option set produces different results

cmake -DCOVERAGE:BOOL=ON ./&& make && make tests && ctest
find . -iname '*gcno' | wc -l
find . -iname '*gcda' | wc -l
grep -Rni 'coverage' CMakeFiles/* | wc -l

outputs

1
0
2

whereas

cmake -DCOVERAGE:BOOL=ON && cmake -DCOVERAGE:BOOL=ON ./ && make && make tests && ctest
find . -iname '*gcno' | wc -l
find . -iname '*gcda' | wc -l
grep -Rni 'coverage' CMakeFiles/* | wc -l

outputs

172
54
3

For more context please see https://github.com/eddyxu/cpp-coveralls/issues/111#issuecomment-403261317