Adds accessor methods to class ClFlags.

Allows one to define explicit overrides in get accessors, based on
compilation features. To show usage, modified SubConstantCalls to
never be enabled if building a minimal llvm2ice.

BUG=None
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/905463003
diff --git a/src/IceCfgNode.cpp b/src/IceCfgNode.cpp
index 8fb06b8..077866b 100644
--- a/src/IceCfgNode.cpp
+++ b/src/IceCfgNode.cpp
@@ -859,7 +859,8 @@
   Func->setCurrentNode(this);
   Ostream &Str = Func->getContext()->getStrEmit();
   Liveness *Liveness = Func->getLiveness();
-  bool DecorateAsm = Liveness && Func->getContext()->getFlags().DecorateAsm;
+  bool DecorateAsm =
+      Liveness && Func->getContext()->getFlags().getDecorateAsm();
   Str << getAsmName() << ":\n";
   std::vector<SizeT> LiveRegCount(Func->getTarget()->getNumRegisters());
   if (DecorateAsm)