Fix to set `old_library` in libtool file only for `staticlib` project

Signed-off-by: OBATA Akio <obache@wizdas.com>
(cherry picked from commit 4596513c45)

qmake/generators/unix/unixmake2.cpp

@@ -1471,7 +1471,11 @@ UnixMakefileGenerator::writeLibtoolFile()
     t << "'\n\n";
 
     t << "# The name of the static archive.\n"
-      << "old_library='" << lname.left(lname.length()-Option::libtool_ext.length()) << ".a'\n\n";
+      << "old_library='";
+    if(project->isActiveConfig("staticlib")) {
+	t << lname.left(lname.length()-Option::libtool_ext.length()) << ".a";
+    }
+    t << "'\n\n";
 
     t << "# Libraries that this one depends upon.\n";
     QStringList libs;