Fix non-usable toolbar on wxPython with GTK3+ in PLCOpenEditor

this problem is related to 'Fix non-usable toolbar on wxPython with
GTK3+' (5927710b). This problem does not happen in Beremiz because
additional necessary self.AUIManager.Update() is called
BeremizIDE. Therefore minimal change in the mentioned commit was
enough for Beremiz, but is not enough for PLCOpenEditor.

          <xsd:attribute name="Compiler" type="xsd:string" use="optional" default="gcc"/>
          <xsd:attribute name="CFLAGS" type="xsd:string" use="optional" default=""/>
          <xsd:attribute name="Linker" type="xsd:string" use="optional" default="gcc"/>
          <xsd:attribute name="LDFLAGS" type="xsd:string" use="optional" default=""/>