Add MSVC 2019 to build, default ctor for static object (#593)

relates #592

appveyor.yml

@@ -1,5 +1,5 @@
 # can use variables like {build} and {branch}
-version: 1.2.{build}
+version: 1.3.{build}
 pull_requests:
   do_not_increment_build_number: true
 
@@ -22,9 +22,14 @@ environment:
     - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2017
       VS_VERSION_MAJOR: 15
       BOOST_ROOT: C:\Libraries\boost_1_66_0
-      #    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019 Preview
-      #      VS_VERSION_MAJOR: 16
-      #      BOOST_ROOT: C:\Libraries\boost_1_66_0
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+      VS_VERSION_MAJOR: 16
+      BOOST_ROOT: C:\Libraries\boost_1_71_0
+
+matrix:
+  exclude:
+    - APPVEYOR_BUILD_WORKER_IMAGE: Visual Studio 2019
+      platform: Win32
 
 platform:
   - Win32

include/cereal/details/static_object.hpp

@@ -94,7 +94,8 @@ namespace cereal
             std::unique_lock<std::mutex> lock;
           #else
           public:
-	          LockGuard(LockGuard const &) = default; // prevents implicit copy ctor warning
+            LockGuard() = default;
+            LockGuard(LockGuard const &) = default; // prevents implicit copy ctor warning
             ~LockGuard() CEREAL_NOEXCEPT {} // prevents variable not used
           #endif
         };

unittests/load_construct.hpp

@@ -234,8 +234,8 @@ void test_memory_load_construct()
       oar( o_constShared2v );
     }
 
-    o_shared3->shared_from_this(); // tests github issue #68
-    o_constShared3->shared_from_this();
+    (void) o_shared3->shared_from_this(); // tests github issue #68
+    (void) o_constShared3->shared_from_this();
 
     decltype(o_shared1) i_shared1;
     decltype(o_shared2) i_shared2;