PPC: 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 44cd9483925ccd1a99464936dd3c2e622d297b0a..42e5a13157fc54a97743d617f22026d6f6b2d9ca 100644
--- a/src/ppc/macro-assembler-ppc.cc
+++ b/src/ppc/macro-assembler-ppc.cc
@@ -570,8 +570,7 @@ 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::kStoreBufferMask));
-  and_(r0, scratch, r0, SetRC);
+  TestBitMask(scratch, StoreBuffer::kStoreBufferMask, r0);
 
   if (and_then == kFallThroughAtEnd) {
     bne(&done, cr0);