[verifier] Do not use llvm::report_fatal_error since it swallows PrettyStackTrace.

I thought this was me being more standard but I keep on hitting this so I am
returning back to an assert(0) version of this. This is only enabled if NDEBUG
is set, so this is ok.

Author: gottesmm

lib/SIL/Verifier/LinearLifetimeCheckerPrivate.h

@@ -208,7 +208,7 @@ class LLVM_LIBRARY_VISIBILITY LinearLifetimeChecker::ErrorBuilder {
     }
 
     llvm::errs() << "Found ownership error?!\n";
-    llvm::report_fatal_error("triggering standard assertion failure routine");
+    assert(0 && "triggering standard assertion failure routine");
   }
 };