Change store buffer overflow check to not rely on the store buffer being (2*Size) aligned.

src/ppc/macro-assembler-ppc.cc

Index: src/ppc/macro-assembler-ppc.cc
diff --git a/src/ppc/macro-assembler-ppc.cc b/src/ppc/macro-assembler-ppc.cc
index 9d3c871e4deee49a00b45c4a42addbe3d1c691e6..c67b2fa2f18ba85d8d37e811457794760ec03cc9 100644
--- a/src/ppc/macro-assembler-ppc.cc
+++ b/src/ppc/macro-assembler-ppc.cc
@@ -570,14 +570,14 @@ void MacroAssembler::RememberedSetHelper(Register object,  // For debug tests.
   StoreP(scratch, MemOperand(ip));
   // Call stub on end of buffer.
   // Check for end of buffer.
-  mov(r0, Operand(StoreBuffer::kStoreBufferOverflowBit));
+  mov(r0, Operand(StoreBuffer::kStoreBufferMask));
   and_(r0, scratch, r0, SetRC);
 
   if (and_then == kFallThroughAtEnd) {
-    beq(&done, cr0);
+    bne(&done, cr0);
   } else {
     DCHECK(and_then == kReturnAtEnd);
-    Ret(eq, cr0);
+    Ret(ne, cr0);
   }
   mflr(r0);
   push(r0);