Fix Math.pow crashes on machines without SSE2.

This is a back-port of r8577 from V8's upstream 3.1 branch.

Fixes #829.

deps/v8/src/ia32/full-codegen-ia32.cc

@@ -2772,8 +2772,12 @@ void FullCodeGenerator::EmitMathPow(ZoneList<Expression*>* args) {
   VisitForStackValue(args->at(0));
   VisitForStackValue(args->at(1));
 
-  MathPowStub stub;
-  __ CallStub(&stub);
+  if (CpuFeatures::IsSupported(SSE2)) {
+    MathPowStub stub;
+    __ CallStub(&stub);
+  } else {
+    __ CallRuntime(Runtime::kMath_pow, 2);
+  }
   context()->Plug(eax);
 }
 

deps/v8/src/version.cc

@@ -35,7 +35,7 @@
 #define MAJOR_VERSION     3
 #define MINOR_VERSION     1
 #define BUILD_NUMBER      8
-#define PATCH_LEVEL       25
+#define PATCH_LEVEL       26
 #define CANDIDATE_VERSION false
 
 // Define SONAME to have the SCons build the put a specific SONAME into the