Meta/Make: allow --locale= and --test= to be given

Meta/Make: allow --locale= and --test= to be given

It often is convenient to run only specific tests while still staying
at the toplevel (some failures only reproduce with particular allocation
patterns, for example).  You can say

    $ Meta/Make --test='1013 91??'

to run only test 1013 and 91xx series.

Similarly, you can give --locale=en_US.UTF-8 or somesuch; earlier we
always run tests in C locale for reproducibility, and the default
stays the same, but sometimes it is useful to run tests in different
locale.