Xcb: remove compile warnings

Change-Id: Ieb3ccd18a2bdde9ef7628a031266004cd55480da
Reviewed-by: Laszlo Agocs <laszlo.agocs@theqtcompany.com>
Fix corner case in preprocessor of QOpenGLShaderProgram

The preprocessor used in QOpenGLShaderProgram to help with determining
where it should add the #line and other #define directives is broken
when parsing the standard Qt Project copyright header.

In a multiline comment if the preprocessor encounters repeated '*'
characters when in a multiline comment, it toggles the state between
MultiLineComment and CommentEnding. This is wrong as every asterisk is
potentially the one before the closing '/' of a multiline comment.

This change fixes this by only going back to the MultiLineComment when
in the CommentEnding state if the character is not another '*'.

Task-number: QTBUG-43240
Change-Id: I114e933026ba5de1c23f3e0399613def59f44961
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>