sparc: get libroot to build

Add various stubs to fix undefined references. No implementation for
anything yet.

Change-Id: I2d398bc2369d099e3a35f0713058d6a5edc6801d
Reviewed-on: https://review.haiku-os.org/c/1138
Reviewed-by: waddlesplash <waddlesplash@gmail.com>

sparc: more platform headers

Previous commit adding these was merged very quickly, so here's one
more...

Change-Id: I23c424db7631db1f0ec48e2d0ae47c8409ae6af2
Reviewed-on: https://review.haiku-os.org/c/1088
Reviewed-by: waddlesplash <waddlesplash@gmail.com>