support older gcov versions (-x -> -p -> none)

[GitMensch]

gcov 7 introduced --hash-filenames (which is used as -x in the script).
gcovr checks once if this option is available (peeking into gcov's help), if it isn't then --preserve-paths (-p) is used instead (actually gcovr also checks for this option in the help and if it isn't available it uses neither of them and output a warning).

Can you please add the same behaviour? This would help in "legacy" environments where you can't easily update gcc (which sadly has to matches gcov).

[xiaoyun94]

do you mean add these into Fake Info ？

[GitMensch]

That would likely need to be done, too, to pass the information.

But before we need to check if the gcov binary used "here" has this option. If it has: output it in "our" help, if it isn't then don't use it around line 80 but use -p instead (or do as gcovr and also check if this is available)...