PR debug/41276
PR debug/41307
* cselib.c (cselib_expand_value_rtx_cb): Document callback
interface.
(cselib_expand_value_rtx_1): Use callback for SUBREGs.  Adjust
for VALUEs, to implement the documented interface.
* var-tracking.c (vt_expand_loc_callback): Handle SUBREGs.
Adjust for VALUEs and anything else, to implement the
documented interface.

From-SVN: r151628