explicitly define destructor to avoid destructing with forward declaration

include/mbgl/style/style.hpp

@@ -28,6 +28,7 @@ public:
 
 public:
     Style();
+    ~Style();
 
     void loadJSON(const uint8_t *const data);
 

src/style/style.cpp

@@ -19,6 +19,11 @@ Style::Style()
     : mtx(std::make_unique<uv::rwlock>()) {
 }
 
+// Note: This constructor is seemingly empty, but we need to declare it anyway
+// because this file includes uv_detail.hpp, which has the declarations necessary
+// for deleting the std::unique_ptr<uv::rwlock>.
+Style::~Style() {}
+
 void Style::updateProperties(float z, timestamp now) {
     uv::writelock lock(mtx);