[firtool] initialize the disableLayerSink flag

When this option was added to the FirtoolOptions struct it was not given
an inital value, which could later be read.  This change also sets the
inital value of the option flag.

lib/Firtool/Firtool.cpp

@@ -527,10 +527,9 @@ struct FirtoolCmdOptions {
                                   "release", "Compile with optimizations")),
       llvm::cl::init(firtool::FirtoolOptions::BuildModeDefault)};
 
-  llvm::cl::opt<bool> disableLayerSink{
-      "disable-layer-sink",
-      llvm::cl::desc("Disable layer sink"),
-  };
+  llvm::cl::opt<bool> disableLayerSink{"disable-layer-sink",
+                                       llvm::cl::desc("Disable layer sink"),
+                                       cl::init(false)};
 
   llvm::cl::opt<bool> disableOptimization{
       "disable-opt",
@@ -770,9 +769,10 @@ circt::firtool::FirtoolOptions::FirtoolOptions()
       allowAddingPortsOnPublic(false), probesToSignals(false),
       preserveAggregate(firrtl::PreserveAggregate::None),
       preserveMode(firrtl::PreserveValues::None), enableDebugInfo(false),
-      buildMode(BuildModeRelease), disableOptimization(false),
-      exportChiselInterface(false), chiselInterfaceOutDirectory(""),
-      vbToBV(false), noDedup(false), companionMode(firrtl::CompanionMode::Bind),
+      buildMode(BuildModeRelease), disableLayerSink(false),
+      disableOptimization(false), exportChiselInterface(false),
+      chiselInterfaceOutDirectory(""), vbToBV(false), noDedup(false),
+      companionMode(firrtl::CompanionMode::Bind),
       disableAggressiveMergeConnections(false), advancedLayerSink(false),
       lowerMemories(false), blackBoxRootPath(""), replSeqMem(false),
       replSeqMemFile(""), extractTestCode(false), ignoreReadEnableMem(false),