Fix crash that could occur if closing the usercard quickly after blocking (#4711)

* Specifically, this adds a caller to the network request, which makes the
success or failure callback not fire.
This has the unintended consequence of the block list not reloading if
the usercard is closed, but it's not a big concern.

* Add unrelated `-DUSE_ALTERNATE_LINKER` cmake option

From https://github.com/heavyai/heavydb/blob/0517d99b467806f6af7b4c969e351368a667497d/CMakeLists.txt#L87-L103

mocks/include/mocks/Helix.hpp

@@ -105,12 +105,14 @@ public:
                 (override));
 
     MOCK_METHOD(void, blockUser,
-                (QString targetUserId, std::function<void()> successCallback,
+                (QString targetUserId, const QObject *caller,
+                 std::function<void()> successCallback,
                  HelixFailureCallback failureCallback),
                 (override));
 
     MOCK_METHOD(void, unblockUser,
-                (QString targetUserId, std::function<void()> successCallback,
+                (QString targetUserId, const QObject *caller,
+                 std::function<void()> successCallback,
                  HelixFailureCallback failureCallback),
                 (override));