[PATCH v2] [BZ #10283] localedef: align fixed maps to SHMLBA

[Roland McGrath]

The fact that SHMLBA is the right size for this is a Linuxism.  It should
not be used directly in generic libc code.  Instead, add a private sysdeps/
header to define a macro or function that yields this larger-than-page size
and explains what uses need to use this size.  If it's then the most
sensible thing for a machine-independent linux/ implementation of this
header to use SHMLBA, then fine.