Mac: check for valid -arch arguments in configure.
Mac: check for valid -arch arguments in configure.

Allow x86 x86_64 ppc ppc64, exit with an error message if something else is passed?

Reviewed-by: nrc

radekp/qt,igor-sfdc/qt-wk,RLovelett/qt,igor-sfdc/qt-wk,RLovelett/qt,RLovelett/qt,KDE/qt,radekp/qt,igor-sfdc/qt-wk,RLovelett/qt,RLovelett/qt,KDE/qt,pruiz/wkhtmltopdf-qt,radekp/qt,radekp/qt,radekp/qt,pruiz/wkhtmltopdf-qt,igor-sfdc/qt-wk,KDE/qt,KDE/qt,radekp/qt,pruiz/wkhtmltopdf-qt,radekp/qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,KDE/qt,radekp/qt,pruiz/wkhtmltopdf-qt,RLovelett/qt,KDE/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,RLovelett/qt,radekp/qt,igor-sfdc/qt-wk,RLovelett/qt,KDE/qt,igor-sfdc/qt-wk,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,pruiz/wkhtmltopdf-qt,RLovelett/qt,radekp/qt,igor-sfdc/qt-wk,KDE/qt,RLovelett/qt,igor-sfdc/qt-wk,pruiz/wkhtmltopdf-qt,RLovelett/qt,igor-sfdc/qt-wk