libgcc, aarch64: Allow for BE platforms in heap trampolines.

This arranges that the byte order of the instruction sequences is
independent of the byte order of memory.

libgcc/ChangeLog:

	* config/aarch64/heap-trampoline.c
	(aarch64_trampoline_insns): Arrange to encode instructions as a
	byte array so that the order is independent of memory byte order.
	(struct aarch64_trampoline): Likewise.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>