Subzero: Make sure alloca with align=0 is handled correctly.

1. Modify dump() to match LLVM.

2. If it weren't for minimum stack alignment, the alignment code would be broken, so add a test in case the alignment code changes.

BUG= none
R=jvoung@chromium.org, kschimpf@google.com

Review URL: https://codereview.chromium.org/557533003

src/IceInst.cpp

diff --git a/src/IceInst.cpp b/src/IceInst.cpp
index cfcaad3..43291ce 100644
--- a/src/IceInst.cpp
+++ b/src/IceInst.cpp
@@ -534,7 +534,8 @@
   dumpDest(Func);
   Str << " = alloca i8, i32 ";
   getSizeInBytes()->dump(Func);
-  Str << ", align " << getAlignInBytes();
+  if (getAlignInBytes())
+    Str << ", align " << getAlignInBytes();
 }
 
 void InstArithmetic::dump(const Cfg *Func) const {