ARM32 vector division lowering.

Enables vector division by scalarization.

Also, removed an assert as suggested by Karl in a previous CL:
https://codereview.chromium.org/1646033002/diff/1/src/IceInstARM32.cpp#newcode717

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4076
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1681003002 .
diff --git a/src/IceTargetLowering.h b/src/IceTargetLowering.h
index 1a0f0b7..55597ca 100644
--- a/src/IceTargetLowering.h
+++ b/src/IceTargetLowering.h
@@ -464,6 +464,9 @@
 
   bool shouldOptimizeMemIntrins();
 
+  void scalarizeArithmetic(InstArithmetic::OpKind K, Variable *Dest,
+                           Operand *Src0, Operand *Src1);
+
   /// SandboxType enumerates all possible sandboxing strategies that
   enum SandboxType {
     ST_None,