[AArch64] Output the pseudo SPACE in asm and object files

Summary: It outputs nothing, but is useful for writing tests, checking asm output.

Reviewers: t.p.northover, ostannard, tellenbach

Reviewed By: tellenbach

Subscribers: tellenbach, kristof.beyls, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69185

Change-Id: I6b58310e9e5632f0976d2000ce975ee28df90ebe