fix warnings and build

include/spdlog/details/backtracer.h

@@ -63,7 +63,7 @@ namespace spdlog {
                 return enabled_.load(std::memory_order_relaxed);
             }
 
-            operator bool() const
+            explicit operator bool() const
             {
                 return enabled();
             }

include/spdlog/details/circular_q.h

@@ -35,7 +35,7 @@ namespace spdlog {
 
             // move cannot be default,
             // since we need to reset head_, tail_, etc to zero in the moved object
-            circular_q(circular_q&& other) SPDLOG_NOEXCEPT:
+            circular_q(circular_q&& other) SPDLOG_NOEXCEPT
             {
                 copy_moveable(std::move(other));
             }

include/spdlog/details/log_msg_buffer.h

@@ -47,10 +47,10 @@ public:
         update_string_views();
     }
 
-    log_msg_buffer &operator=(log_msg_buffer &other)
+    log_msg_buffer &operator=(const log_msg_buffer &other)
     {
         log_msg::operator=(other);
-        buffer.append(other.buffer.begin(), other.buffer.end());
+        buffer.append(other.buffer.data(), other.buffer.data() + other.buffer.size());
         update_string_views();
         return *this;
     }