ReleaseChannel: only query the OS version on updater platforms

The in-client updater only ships assets for macOS and Windows, but the
host system version was still being resolved on every platform, including
Linux where it is never used. Compute it only under the Q_OS_MACOS /
Q_OS_WIN guards.

cockatrice/src/client/network/update/client/release_channel.cpp

@@ -30,6 +30,7 @@
 namespace
 {
 
+#if defined(Q_OS_MACOS) || defined(Q_OS_WIN)
 // QSysInfo::productVersion() is not guaranteed to start with a number, e.g. it returns
 // "Server 2022" on Windows Server. Use the first numeric token as the major host version.
 std::optional<int> getProductVersionMajor()
@@ -45,6 +46,7 @@ std::optional<int> getProductVersionMajor()
     }
     return version;
 }
+#endif
 
 } // namespace
 
@@ -76,7 +78,13 @@ std::optional<int> ReleaseChannel::getTargetVersionForCurrentOS(const QString &f
 
     const QRegularExpression *regex = nullptr;
 
-    static const std::optional<int> systemVersion = getProductVersionMajor();
+    // Only platforms shipping updater assets (macOS, Windows) need the host version
+    static const std::optional<int> systemVersion =
+#if defined(Q_OS_MACOS) || defined(Q_OS_WIN)
+        getProductVersionMajor();
+#else
+        std::nullopt;
+#endif
 
     if (!systemVersion) {
         return std::nullopt;