Beginning of locale-loading code committed

[Rich Felker <dalias@libc.org>]

Last night I committed the locale loading code as commit
6cb4f91db7a5dc3bca63037ddc5f998a08dc3fb0. It doesn't do much
interesting yet (since the loaded data is not used) but you can
observe its behavior via calls to setlocale to set and query the
locale category values.

One thing I left out at this point is a default locale path when
MUSL_LOCPATH is not set. We could consider adding it later, but as
long as the locale code is new and experimental, I tend to think it's
better to have all locale-loading functionality disabled unless the
user/admin/distro has explicitly set a locale path. This will avoid
unexpected changes in behavior for existing deployments upgrading to
1.1.4 (except possibly the byte-based C locale, if we merge it, since
it's of course built-in). It also avoids imposing any policy, even a
default one. Of course the disadvantage is that suid programs have no
way of using locale, so we will have to find some way of providing a
default (or a way to load a path from the filesystem) at some point.

Rich