Allow non-host-platform libraries in Add Library wizard

Since much of the available UI and behavior depends on which platform's
library we start with, let the user choose a platform filter.
Default is the host OS.

Task-number: QTCREATORBUG-17995
Change-Id: Ic8bec7ac30eecf08c1684da4f2823a8add8f6d20
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/libs/utils/pathchooser.cpp

@@ -655,6 +655,7 @@ QString PathChooser::promptDialogTitle() const
 void PathChooser::setPromptDialogFilter(const QString &filter)
 {
     d->m_dialogFilter = filter;
+    d->m_lineEdit->validate();
 }
 
 QString PathChooser::promptDialogFilter() const