AIX: Fix 'may be used uninitialized' compiler errors

src/compiler/ppc/instruction-selector-ppc.cc

Index: src/compiler/ppc/instruction-selector-ppc.cc
diff --git a/src/compiler/ppc/instruction-selector-ppc.cc b/src/compiler/ppc/instruction-selector-ppc.cc
index 03824042a3378f0a9581e025f78b3adb082496c5..d211a439135c7fe761ded2abb6a13a1e106e61ff 100644
--- a/src/compiler/ppc/instruction-selector-ppc.cc
+++ b/src/compiler/ppc/instruction-selector-ppc.cc
@@ -417,8 +417,8 @@ static inline bool IsContiguousMask64(uint64_t value, int* mb, int* me) {
 void InstructionSelector::VisitWord32And(Node* node) {
   PPCOperandGenerator g(this);
   Int32BinopMatcher m(node);
-  int mb;
-  int me;
+  int mb = 0;
+  int me = 0;
   if (m.right().HasValue() && IsContiguousMask32(m.right().Value(), &mb, &me)) {
     int sh = 0;
     Node* left = m.left().node();
@@ -456,8 +456,8 @@ void InstructionSelector::VisitWord32And(Node* node) {
 void InstructionSelector::VisitWord64And(Node* node) {
   PPCOperandGenerator g(this);
   Int64BinopMatcher m(node);
-  int mb;
-  int me;
+  int mb = 0;
+  int me = 0;
   if (m.right().HasValue() && IsContiguousMask64(m.right().Value(), &mb, &me)) {
     int sh = 0;
     Node* left = m.left().node();