fix quoting of qmake parameters in 'qmake' target

we need to do full shell quoting, not the limited whitespace quoting.

Task-number: QTBUG-46224
Change-Id: I41bc9aee556ca680dce0875b58159a31db962452
Reviewed-by: Joerg Bornemann <joerg.bornemann@theqtcompany.com>

qmake/generators/makefile.cpp

@@ -2240,7 +2240,7 @@ QString MakefileGenerator::buildArgs()
     QString ret;
 
     foreach (const QString &arg, Option::globals->qmake_args)
-        ret += " " + escapeFilePath(arg);
+        ret += " " + shellQuote(arg);
     return ret;
 }