[GCC, AARCH64] Add GNU note section with BTI and PAC.

[GCC, AARCH64] Add GNU note section with BTI and PAC.

This patch adds the GNU NOTE section to the BTI and/or PAC
enabled objects for linux targets.

The patches for needed for these in binutils are already approved
and committed.
https://sourceware.org/ml/binutils/2019-03/msg00072.html

*** gcc/ChangeLog ***

2018-04-23  Sudakshina Das  <sudi.das@arm.com>

	* config/aarch64/aarch64-linux.h (TARGET_ASM_FILE_END): Define for
	AArch64.
	(aarch64_file_end_indicate_exec_stack): Add gnu note section.

gcc/testsuite/ChangeLog:

2018-04-23  Sudakshina Das  <sudi.das@arm.com>

	* gcc.target/aarch64/bti-1.c: Add scan directive for gnu note section
	for linux targets.
	* gcc.target/aarch64/va_arg_1.c: Update scan directive to not clash
	with GNU note section.

From-SVN: r270515