This kills both a hack and the regression discussed on gdb at dot Instead of
returning the value of the register and the register number, if the
expression evaluator only returns the register number, we can use
value_from_register. This way we share multi-register variable handling
with the non-LOC_COMPUTED case.
This patch removes a FIXME and an interface I didn't much like (the lval
argument to dwarf_expr_read_reg) so I'm pretty happy with it. Everything
should go back to working that worked before.