In my case the issue was a wrong build command for meson. I.e:

meson setup build --reconfigure -Db_coverage=true -Dc_args=-Og,-w

Is wrong, and should instead be:

meson setup build --reconfigure -Db_coverage=true -Dc_args=-Og

Adding an extra -w causes meson to pass that -w to a default C compiler as a test, which causes the compiler to return an exception. Meson then decides that the compiler doesn't work - and announces that the compiler for "c" is not specified for the host machine.