By using the __BYTE_ORDER__ predefined macro we don't need the
determine_endianness function anymore.

Regtested on x86_64-pc-linux-gnu.

libgfortran/ChangeLog:

2017-11-22  Janne Blomqvist  <jb@gcc.gnu.org>

        PR libfortran/83097
	* io/inquire.c (inquire_via_unit): Use __BYTE_ORDER__ predefined
	macro.
	* io/open.c (st_open): Likewise.
	* io/transfer.c (data_transfer_init): Likewise.
	* io/write.c (btoa_big): Likewise.
	(otoa_big): Likewise.
	(ztoa_big): Likewise.
	* libgfortran.h (big_endian): Remove variable.
	(GFOR_POINTER_TO_L1): Use __BYTE_ORDER__ macro.
	* runtime/main.c (determine_endianness): Remove function.
	(init): Remove call to determine_endianness.
	* runtime/minimal.c: Remove setting big_endian variable.

From-SVN: r255072