Fix the build of -qt-freetype

The symbol must be exported from QtGui for the plugins to be able to
see it.

Also, fix the build in namespaced case: cannot use extern in
QtPlatformSupport because it's not compiled into the Qt namespace.

Change-Id: I029533f3524e3cbf6c87aed79c1f2e7b55aebb9b
Reviewed-by: Samuel Rødal <samuel.rodal@nokia.com>

src/gui/text/qfontengine_ft_p.h

@@ -364,6 +364,7 @@ inline QFontEngineFT::Glyph *QFontEngineFT::QGlyphSet::getGlyph(glyph_t index, Q
     return glyph_data.value(GlyphAndSubPixelPosition(index, subPixelPosition));
 }
 
+extern Q_GUI_EXPORT FT_Library qt_getFreetype();
 
 QT_END_NAMESPACE
 

src/platformsupport/fontdatabases/fontconfig/qfontconfigdatabase.cpp

@@ -670,7 +670,6 @@ static FcPattern *queryFont(const FcChar8 *file, const QByteArray &data, int id,
     if (data.isEmpty())
         return FcFreeTypeQuery(file, id, blanks, count);
 
-    extern FT_Library qt_getFreetype();
     FT_Library lib = qt_getFreetype();
 
     FcPattern *pattern = 0;