meson: omit bash completion, with custom prefix
In order for bash completions to work, they must be installed in the
respective folder. Often that folder is writable only by root.
In order words, using a command line the following now is successful,
providing indicative warning message.
meson builddir --prefix `pwd`/inst
...
meson.build:140: WARNING: User provided prefix '.../inst' differs from bash-completion one '/usr'. Disabling completion.
Reported-by: Pekka Paalanen <pekka.paalanen@collabora.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>