Add a way to pass in a preconstructed value to ManagedStatic (#2175)

A lot of our cases don't need the lazy construction, but do need manual destruction.

wpiutil/src/main/native/cpp/llvm/ManagedStatic.cpp

@@ -30,6 +30,22 @@ static wpi::mutex* getManagedStaticMutex() {
   return ManagedStaticMutex;
 }
 
+void ManagedStaticBase::RegisterManagedStatic(void* created,
+                                              void (*Deleter)(void*)) const {
+  std::scoped_lock Lock(*getManagedStaticMutex());
+
+  if (!Ptr.load(std::memory_order_relaxed)) {
+    void *Tmp = created;
+
+    Ptr.store(Tmp, std::memory_order_release);
+    DeleterFn = Deleter;
+
+    // Add to list of managed statics.
+    Next = StaticList;
+    StaticList = this;
+  }
+}
+
 void ManagedStaticBase::RegisterManagedStatic(void *(*Creator)(),
                                               void (*Deleter)(void*)) const {
   assert(Creator);

wpiutil/src/main/native/include/wpi/ManagedStatic.h

@@ -43,6 +43,7 @@ protected:
   mutable const ManagedStaticBase *Next;
 
   void RegisterManagedStatic(void *(*creator)(), void (*deleter)(void*)) const;
+  void RegisterManagedStatic(void *created, void (*deleter)(void*)) const;
 
 public:
   /// isConstructed - Return true if this object has not been created yet.
@@ -60,6 +61,12 @@ template <class C, class Creator = object_creator<C>,
           class Deleter = object_deleter<C>>
 class ManagedStatic : public ManagedStaticBase {
 public:
+  ManagedStatic() = default;
+
+  ManagedStatic(C* created, void(*deleter)(void*)) {
+    RegisterManagedStatic(created, deleter);
+  }
+
   // Accessors.
   C &operator*() {
     void *Tmp = Ptr.load(std::memory_order_acquire);