OE manages all the compile flags, so we don't want meson to inject its
own flags. Currently, it's injecting -O0 and causing build breaks when
security flags are enabled (because _FORTIFY_SOURCE requires an
optimized build and meson defaults to a debug -O0 build).
Add --buildtype plain so meson will not add its own optimization flags.
Signed-off-by: Martin Kelly <mkelly@xevo.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
