Subzero. Adds a pass for target-specific helper call generation.

This pass gives Targets the ability to pre-lower high-level
instructions that will later be lowered to a target-specific helper,
e.g., 64-bit division on targets that can't natively handle them.

This is a pre-requirement for correct outargs pre-allocation during
function prolog.

R=sehr@chromium.org

Review URL: https://codereview.chromium.org/1455033005 .

src/IceTargetLoweringARM32.cpp

diff --git a/src/IceTargetLoweringARM32.cpp b/src/IceTargetLoweringARM32.cpp
index 24cced8..60d3a37 100644
--- a/src/IceTargetLoweringARM32.cpp
+++ b/src/IceTargetLoweringARM32.cpp
@@ -238,6 +238,7 @@
 
   // TODO(stichnot): share passes with X86?
   // https://code.google.com/p/nativeclient/issues/detail?id=4094
+  genTargetHelperCalls();
 
   // Do not merge Alloca instructions, and lay out the stack.
   static constexpr bool SortAndCombineAllocas = false;
@@ -344,6 +345,7 @@
   TimerMarker T(TimerStack::TT_Om1, Func);
 
   // TODO: share passes with X86?
+  genTargetHelperCalls();
 
   // Do not merge Alloca instructions, and lay out the stack.
   static constexpr bool SortAndCombineAllocas = false;