[arm] Make CEntryStub's handling of triple return values more robust.

At the moment the code assumes C-function returns the address of the
struct with the values. Unfortunately, the arm ABI does not guarantee that.
After this CL, we do not assume that, and instead just take the value from the stack.

BUG=chromium:611885
LOG=n

Review-Url: https://codereview.chromium.org/2000713002
Cr-Commit-Position: refs/heads/master@{#36415}

src/arm/code-stubs-arm.cc

@@ -1055,9 +1055,9 @@ void CEntryStub::Generate(MacroAssembler* masm) {
   if (result_size() > 2) {
     DCHECK_EQ(3, result_size());
     // Read result values stored on stack.
-    __ ldr(r2, MemOperand(r0, 2 * kPointerSize));
-    __ ldr(r1, MemOperand(r0, 1 * kPointerSize));
-    __ ldr(r0, MemOperand(r0, 0 * kPointerSize));
+    __ ldr(r2, MemOperand(sp, 2 * kPointerSize));
+    __ ldr(r1, MemOperand(sp, 1 * kPointerSize));
+    __ ldr(r0, MemOperand(sp, 0 * kPointerSize));
   }
   // Result returned in r0, r1:r0 or r2:r1:r0 - do not destroy these registers!