configure.ac: Move AC_ARG_WITH checks for native-system-header-dir...

configure.ac: Move AC_ARG_WITH checks for native-system-header-dir...

2015-07-17  Yvan Roux  <yvan.roux@linaro.org>
	    Matthias Klose  <doko@ubuntu.com>

	* configure.ac: Move AC_ARG_WITH checks for native-system-header-dir,
	build-sysroot, sysroot from the `Miscenalleous configure options' to
	the `Directories' section and strip trailing `/' from with_sysroot.
	(gcc_gxx_include_dir): Don't strip a `/' sysroot value.
	* configure: Regenerated.

Co-Authored-By: Matthias Klose <doko@ubuntu.com>
From-SVN: r225921