LanguageClient: Fix qbs mingw build

Change-Id: Idb7102597a9a7cdf8a8cd5cd1ce249770e559c16
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/languageclient/languageclient.qbs

@@ -67,5 +67,10 @@ QtcPlugin {
         "snippet.h",
     ]
 
+    Properties {
+        condition: qbs.toolchain.contains("mingw")
+        cpp.cxxFlags: "-Wa,-mbig-obj"
+    }
+
     Export { Depends { name: "LanguageServerProtocol" } }
 }