Fix various configure time warnings about missing QT_BEGIN_NAMESPACE

We now have a couple of global.h headers that do only start with 'q'.
We can't change this anymore, so let's just accommodate for that.

This fixes the following warnings

  qtserialport/src/serialport/qserialportglobal.h does not include QT_BEGIN_NAMESPACE
  qtwebsockets/src/websockets/qwebsockets_global.h does not include QT_BEGIN_NAMESPACE
  qtwebchannel/src/webchannel/qwebchannelglobal.h does not include QT_BEGIN_NAMESPACE

Pick-to: 6.2
Fixes: QTBUG-97831
Change-Id: I12aae13eb0d782d366cb84999392a544c30cdd79
Reviewed-by: Alexey Edelev <alexey.edelev@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

Author: kkoehne

libexec/syncqt.pl

@@ -363,7 +363,7 @@ sub check_header {
     return if ($ignore_for_include_check{$header});
     if ($public_header) {
         $header_skip_qt_begin_namespace_test = $header &&
-             ($ignore_for_qt_begin_namespace_check{$header} || $header =~ m,(^|/)qt\w+global\.h$,);
+             ($ignore_for_qt_begin_namespace_check{$header} || $header =~ m,(^|/)q\w+global\.h$,);
     }
 
     local $/ = "\x0a";