Reserve G1 for frame offset stuff and use it to handle large stack frames.

Reserve G1 for frame offset stuff and use it to handle large stack frames.
For example, instead of emitting this:

test:
        save -40112, %o6, %o6   ;; imm too large
        add %i6, -40016, %o0    ;; imm too large
        call caller
        nop
        restore %g0, %g0, %g0
        retl
        nop

emit this:

test:
        sethi 4194264, %g1
        or %g1, 848, %g1
        save %o6, %g1, %o6
        sethi 4194264, %g1
        add %g1, %i6, %g1
        add %i1, 944, %o0
        call caller
        nop
        restore %g0, %g0, %g0
        retl
        nop

which doesn't cause the assembler to barf.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@24880 91177308-0d34-0410-b5e6-96231b3b80d8