Add support for GCC 14 condition coverage (MC/DC)

[sebhub]

GCC 14 will support condition coverage:

https://gcc.gnu.org/onlinedocs/gcc/Instrumentation-Options.html#index-fcondition-coverage

The corresponding GCC commit is:

https://gcc.gnu.org/git/?p=gcc.git;a=commit;h=08a52331803f66a4aaeaedd278436ca8eac57b50

Support was added to the gcov tool to show the condition coverage information:

https://gcc.gnu.org/onlinedocs/gcc/Invoking-Gcov.html

gcov --conditions:

        3:   17:void fn (int a, int b, int c, int d) {
        3:   18:    if ((a && (b || c)) && d)
conditions covered 3/8
condition  0 not covered (true false)
condition  1 not covered (true)
condition  2 not covered (true)
condition  3 not covered (true)
        1:   19:        x = 1;
        -:   20:    else
        2:   21:        x = 2;
        3:   22:}

gcov --conditions --json-format:

"conditions": [
    {
        "not_covered_false": [
            0
        ],
        "count": 8,
        "covered": 3,
        "not_covered_true": [
            0,
            1,
            2,
            3
        ]
    }
],

It would be nice if gcovr could also present this information.

[Spacetown]

We're waiting already for the release of version 14 to finish #766

[Spacetown]

@latk How shall we continue with the decision coverage? With gcc 14 this wouldn't be needed anymore.

[latk]

With gcc 14 this wouldn't be needed anymore.

It will be quite some time until GCC 14 is widely used. Gcovr claims support for GCC 5.x (!), and Clang is also a thing.

It would be great to use this new GCC feature whenever available, but to continue supporting a reasonable range of other compilers.