Unify XDEBUG and EXPENSIVE_CHECKS (into the latter), and add an option to the cmake build to enable them.

Summary:
Historically, we had a switch in the Makefiles for turning on "expensive
checks". This has never been ported to the cmake build, but the
(dead-ish) code is still around.

This will also make it easier to turn it on in buildbots.

Reviewers: chandlerc

Subscribers: jyknight, mzolotukhin, RKSimon, gberry, llvm-commits

Differential Revision: http://reviews.llvm.org/D19723

llvm-svn: 268050
diff --git a/llvm/lib/Target/ARM/ARMFrameLowering.cpp b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
index 909a728..808a21f 100644
--- a/llvm/lib/Target/ARM/ARMFrameLowering.cpp
+++ b/llvm/lib/Target/ARM/ARMFrameLowering.cpp
@@ -2155,7 +2155,7 @@
 
   PrevStackMBB->addSuccessor(McrMBB);
 
-#ifdef XDEBUG
+#ifdef EXPENSIVE_CHECKS
   MF.verify();
 #endif
 }