Missing support for gcc -g3

[byron-hawkins]

The debug builds in Meson use flag -g which does not include all debug symbols. For example, we cannot use macros in GDB on a Meson debug build. The workaround is to explicitly set -g3 as a cflag. Perhaps there are pros and cons to using -g3, but I don't know of any cons.

[jpakkane]

I don't know of any cons.

The debug data created by -g3 is massively bigger than plain -g and generating it takes longer (I think, have not measured).

[tristan957]

@byron-hawkins I think the best way to support this is to have a debug_level option. GCC supports 0-3 for instance. I think clang does as well.