Do not strip debug info for CMAKE_BUILD_TYPE=RelWithDebInfo

Do not strip debug info for CMAKE_BUILD_TYPE=RelWithDebInfo

If `CMAKE_BUILD_TYPE` is set to `RelWithDebInfo` the debug information
should not be stripped. Currently `strip -x` is called when
`RelWithDebInfo` is set. A useless `echo` is called when `Debug` is set.

Skip `strip -x` when `CMAKE_BUILD_TYPE` is set to `Debug` or
`RelWithDebInfo`.

Forwarded: https://github.com/audacity/audacity/pull/3672
Signed-off-by: Benjamin Drung <benjamin.drung@canonical.com>
Gbp-Pq: Name Do-not-strip-debug-info-for-CMAKE_BUILD_TYPE-RelWithDebIn.patch