CTest: Handle non-coverage lines in gcov files
This implements a TODO in gcov file handling.
To see an example of lines that need to be skipped you can look at the man page of gcov: https://www.man7.org/linux/man-pages/man1/gcov.1.html
The lines that need to be processed seem to always start with a space and have a colon in the 9th place. For coverage lines to not have a space in the first place the line needs to be run MANY times.