QtSupport: Fix Qt version detection

Amends 84befc2 which was too strict.

Fixes: QTCREATORBUG-26123
Change-Id: I3767ba0fb4723c77cfb0e8b1932ff6adfc8e9ac2
Reviewed-by: David Schulz <david.schulz@qt.io>

src/plugins/qtsupport/baseqtversion.cpp

@@ -1833,11 +1833,12 @@ bool BaseQtVersionPrivate::queryQMakeVariables(const FilePath &binary, const Env
     QByteArray output;
     output = runQmakeQuery(binary, env, error);
 
-    if (!output.startsWith('Q')) { // Is it always "QT_SYSROOT="?
+    if (!output.contains("QMAKE_VERSION:")) {
         // Some setups pass error messages via stdout, fooling the logic below.
         // Example with docker/qemu/arm "OCI runtime exec failed: exec failed: container_linux.go:367:
         // starting container process caused: exec: "/bin/qmake": stat /bin/qmake: no such file or directory"
         // Since we have a rough idea on what the output looks like we can work around this.
+        // Output does not always start with QT_SYSROOT, see QTCREATORBUG-26123.
         *error = QString::fromUtf8(output);
         return false;
     }