Debug Info Verifier: disable it by default.

Debug info verifier is part of the verifier which is a Function Pass.
Tot currently tries to pull all reachable debug info MDNodes in each function,
which is too time-consuming. The correct fix seems to be separating debug info
verification to its own module pass.

I will disable the debug info verifier until a correct fix is found.

For Bill's testing case, enabling debug info verifier increase compile
time from 11s to 11m.

llvm-svn: 194986
diff --git a/llvm/lib/IR/Verifier.cpp b/llvm/lib/IR/Verifier.cpp
index 3331a37..0bcb118 100644
--- a/llvm/lib/IR/Verifier.cpp
+++ b/llvm/lib/IR/Verifier.cpp
@@ -78,7 +78,7 @@
 using namespace llvm;
 
 static cl::opt<bool> DisableDebugInfoVerifier("disable-debug-info-verifier",
-                                              cl::init(false));
+                                              cl::init(true));
 
 namespace {  // Anonymous namespace for class
   struct PreVerifier : public FunctionPass {