In 2ae3c890bd923b4c39bba3d2e2f2d75eca5dcc06, -Wimplicit-fallthrough=0 was added to get the build to pass. This option is equivalent to -Wno-implicit-fallthrough, and the latter is compatible with clang (while the former is not). Fixes issue #7546. Signed-off-by: Damien George <damien@micropython.org>