Disable lifetime dependence diagnostics by default.

For testing and experimentation, use:
-Xllvm enable-lifetime-dependence-diagnostics

This will be enabled by default once ~Escapable can be used without
building the standard library with the experimental NonescapableTypes
feature.

For now, we want to enable NonescapableTypes for bootstrapping without
forcing diagnostics to run all the time.

Author: atrick

lib/SILOptimizer/PassManager/PassPipeline.cpp

@@ -70,9 +70,9 @@ llvm::cl::opt<bool>
                           llvm::cl::desc("Enable the DestroyHoisting pass."));
 
 llvm::cl::opt<bool>
-DisableLifetimeDependenceDiagnostics(
-  "disable-lifetime-dependence-diagnostics", llvm::cl::init(false),
-  llvm::cl::desc("Disable lifetime dependence diagnostics."));
+EnableLifetimeDependenceDiagnostics(
+  "enable-lifetime-dependence-diagnostics", llvm::cl::init(false),
+  llvm::cl::desc("Enable lifetime dependence diagnostics."));
 
 //===----------------------------------------------------------------------===//
 //                          Diagnostic Pass Pipeline
@@ -168,7 +168,7 @@ static void addMandatoryDiagnosticOptPipeline(SILPassPipelinePlan &P) {
   P.addMoveOnlyChecker();
 
   // Check ~Escapable.
-  if (!DisableLifetimeDependenceDiagnostics) {
+  if (EnableLifetimeDependenceDiagnostics) {
     P.addLifetimeDependenceDiagnostics();
   }
   if (EnableDeinitDevirtualizer)