[scripts] ext-toolchain.sh:

	- use GCC's own idea of the target name (-dumpmachine)
	- display help if called without args
	- add copyright foo
	- remove some leftover flag handling code


git-svn-id: svn://svn.openwrt.org/openwrt/trunk@29769 3c298f89-4303-0410-b956-a3cf2f4a3e73