When compiling glibc we found that the GOT register was being allocated
r9 when the instruction was still set_got_tmp.  That is a problem
because r9 is the Link Register (LR) in OpenRISC which is used/clobbered
in set_got.  We cannot use r9 as the GOT register.  Also, we cannot
simply say set_got_tmp clobbers r9 as this is the reason for having the
temporary set_got_tmp.

Fix by using a register class constraint that does not allow r9 during
register allocation.

gcc/ChangeLog:

        * config/or1k/constraints.md (t): New constraint.
        * config/or1k/or1k.h (GOT_REGS): New register class.
        * config/or1k/or1k.md (set_got_tmp, set_got): Use t contraint.

From-SVN: r275242