[oe] Cmake cross-compile file

[Valentin Longchamp]

Hello,

I had already posted this patch earlier bit I got no comment. It allows cmake
to work with cross-compile files where the needed paths, options and programs
are given, which is the recommended way of doing cross-compilation with cmake
according to their documentation.

Furthermore, you can add additionnal path in individual recipes by writing into
the cross-compile file in the do_generate_toolchain_file_append() task as done 
below for qt4 for instance.

do_generate_toolchain_file_append() {
	echo "set( QT_HEADERS_DIR ${OE_QMAKE_INCDIR_QT} CACHE STRING \"Qt4 include dir\" )" >> ${WORKDIR}/toolchain.cmake
	echo "set( QT_LIBRARY_DIR ${OE_QMAKE_LIBDIR_QT} CACHE STRING \"Qt4 library dir\" )" >> ${WORKDIR}/toolchain.cmake
	echo "set( QT_QMAKE_EXECUTABLE ${OE_QMAKE_QMAKE} CACHE STRING \"qmake2 binary\" )" >> ${WORKDIR}/toolchain.cmake
	echo "set( QT_MOC_EXECUTABLE ${OE_QMAKE_MOC} CACHE STRING \"Qt4 moc binary\" )" >> ${WORKDIR}/toolchain.cmake
	echo "set( QT_UIC_EXECUTABLE ${OE_QMAKE_UIC} CACHE STRING \"Qt4 uic binary\" )" >> ${WORKDIR}/toolchain.cmake
	echo "set( QT_UIC3_EXECUTABLE ${OE_QMAKE_UIC3} CACHE STRING \"Qt4 uic3 binary\" )" >> ${WORKDIR}/toolchain.cmake
	echo "set( QT_RCC_EXECUTABLE ${OE_QMAKE_RCC} CACHE STRING \"Qt4 rcc binary\" )" >> ${WORKDIR}/toolchain.cmake
	echo "set( QT_DBUSXML2CPP_EXECUTABLE ${OE_QMAKE_QDBUSXML2CPP} CACHE STRING \"Qt4 dbus xml2cpp binary\" )" >> ${WORKDIR}/toolchain.cmake
	echo "set( QT_DBUSCPP2XML_EXECUTABLE ${OE_QMAKE_QDBUSCPP2XML} CACHE STRING \"Qt4 dbus cpp2xml binary\" )" >> ${WORKDIR}/toolchain.cmake
	echo "set( QT_LRELEASE_EXECUTABLE ${OE_QMAKE_LRELEASE} CACHE STRING \"Qt4 lrelease binary\" )" >> ${WORKDIR}/toolchain.cmake
	echo "set( QT_LUPDATE_EXECUTABLE ${OE_QMAKE_LUPDATE} CACHE STRING \"Qt4 lupdate binary\" )" >> ${WORKDIR}/toolchain.cmake 
}

I have been using it in my overlay for quite some time with various cmake based
recipes we have here and I definitely think it would deserve OE inlcusion.

Comment welcome

Val