Subzero WASM: avoid needless comparisons, add bounds check flag option

src/IceClFlags.def

Index: src/IceClFlags.def
diff --git a/src/IceClFlags.def b/src/IceClFlags.def
index cfbf9aab6357a0a5258add2fdfe6bdd2413b6893..74b6a623110c41244c03dfdda06fdddfe9b00089 100644
--- a/src/IceClFlags.def
+++ b/src/IceClFlags.def
@@ -345,7 +345,10 @@ struct dev_list_flag {};
                                                                                \
   X(VerboseFocusOnString, std::string, dev_opt_flag, "verbose-focus",          \
     cl::desc("Override with -verbose=none except for specified functions"),    \
-    cl::init(":"))
+    cl::init(":"))                                                             \
+                                                                               \
+  X(WasmNoBoundsCheck, bool, dev_opt_flag, "wasm-disable-bounds-check",        \

[Jim Stichnoth, 2016/05/06 20:37:51]

Minor nit/request.  Can we call this "-wasm-bounds-check" with cl::init(true)? 
This sets up for the future experiment I proposed where you can run with
"-wasm-bounds-check=10" and have it insert 10 copies of bounds checks to see the
performance impact.

[Eric Holk, 2016/05/06 20:56:21]

Done.

+    cl::desc("Omit bounds checking code in WASM frontend"))
 //#define X(Name, Type, ClType, ...)
 
 } // end of namespace Ice