Permit multiple sysroot directories

Hi,

the goal is to have both "" and "target:" as the default gdb_sysroot, in this
order.  Therefore permit multiple directory components of gdb_sysroot.


Jan


gdb/ChangeLog
2015-08-18  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* NEWS (Changes since GDB 7.10): Mention set sysroot and show sysroot.
	* solib.c: Include source.h.
	(solib_find_1): Rename to ...
	(solib_find_2): ... here and change the sysroot variable to parameter.
	(solib_find_1): Call it using dirnames_to_char_ptr_vec_target_exc.
	* source.c (dirnames_to_char_ptr_vec_target_exc): New function.
	* source.h (dirnames_to_char_ptr_vec_target_exc): New declaration.

gdb/doc/ChangeLog
2015-08-18  Jan Kratochvil  <jan.kratochvil@redhat.com>

	* gdb.texinfo (Files): Permit set sysroot and show sysroot to have
	multiple components.