Building with -Os produces linknamespace and localplt failures for,
among other functions, gnu_dev_major, gnu_dev_minor and
gnu_dev_makedev.
The issue is that those functions are not inlined when building with
-Os. While one could force them to be inlined in that case, it seems
more natural to fix this issue similarly to other namespace issues.
Thus, this patch makes gnu_dev_* into weak aliases for hidden symbols
__gnu_dev_*; __gnu_dev_* are then defined as inlines in the internal
include/sys/sysmacros.h, and uses of gnu_dev_* (often via the macros
major, minor and makedev) for which there are namespace issues are
changed to use __gnu_dev_*; where there are no namespace issues, use
of libc_hidden_proto serves to avoid unnecessary local PLT entry use.