Don't reserve R2 on Darwin/PPC

Now that only the register-scavenger version of the CR spilling code remains,
we no longer need the Darwin R2 hack. Darwin can use R0 as a spare register in
any case where the System V ABI uses it (R0 is special architecturally, and so
is reserved under all common ABIs).

A few test cases needed to be updated to reflect the register-allocation changes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@176868 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/CodeGen/PowerPC/varargs.ll b/test/CodeGen/PowerPC/varargs.ll
index 1769be9..90f0480 100644
--- a/test/CodeGen/PowerPC/varargs.ll
+++ b/test/CodeGen/PowerPC/varargs.ll
@@ -8,15 +8,16 @@
 }
 
 ; P32: test1:
-; P32: 	lwz r4, 0(r3)
-; P32:	addi r5, r4, 4
-; P32:	stw r5, 0(r3)
-; P32:	lwz r3, 0(r4)
-; P32:	blr 
+; P32: lwz r2, 0(r3)
+; P32: addi r4, r2, 4
+; P32: stw r4, 0(r3)
+; P32: lwz r3, 0(r2)
+; P32: blr 
 
 ; P64: test1:
-; P64: ld r4, 0(r3)
-; P64: addi r5, r4, 8
-; P64: std r5, 0(r3)
-; P64: ld r3, 0(r4)
-; P64: blr
+; P64: ld r2, 0(r3)
+; P64: addi r4, r2, 8
+; P64: std r4, 0(r3)
+; P64: ld r3, 0(r2)
+; P64: blr 
+