don't flush qmake command line twice

otherwise variable assignments (including -config options) from
$QMAKEFLAGS are lost.

Change-Id: I818e9372d2b0ff44333dc3eb8fc3420f84ab01c5
Reviewed-by: Joerg Bornemann <joerg.bornemann@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
(cherry picked from qtbase/864e1ceaf628e823103ae2d28d2c983400ba38c7)

src/linguist/shared/qmakeglobals.h

@@ -99,6 +99,8 @@ public:
     QString pwd;
     QStringList precmds, preconfigs, postcmds, postconfigs;
     bool after;
+
+    void flush() { after = false; }
 };
 
 class QMAKE_EXPORT QMakeGlobals