[NetBSD] Add support for the Arm EABI.

[NetBSD] Add support for the Arm EABI.

This is a roll-up of a set of changes needed to support the Arm EABI on NetBSD.

2019-06-14  Matt Thomas  <matt@3am-software.com>
	    Matthew Green  <mrg@eterna.com.au>
	    Nick Hudson  <skrll@netbsd.org>
	    Maya Rashish  <coypu@sdf.org>
	    Richard Earnshaw  <rearnsha@arm.com>

gcc:

	* config.gcc (arm*-*-netbsdelf*) Add support for EABI configuration.
	* config.host (arm*-*-netbsd*): Use driver-arm.o on native NetBSD.
	* config/arm/netbsd-eabi.h: New file.
	* config/arm/netbsd-elf.h (TARGET_OS_CPP_BUILTINS): Undefine before
	redefining.
	(SUBTARGET_EXTRA_ASM_SPEC): Don't pass -matpcs to the assembler.
	* config/netbsd-elf.h (NETBSD_LINK_LD_ELF_SO_SPEC): New define.
	(NETBSD_SUBTARGET_EXTRA_SPECS): New define.
	(SUBTARGET_EXTRA_SPECS): Define to NETBSD_SUBTARGET_EXTRA_SPECS.

libatomic:
	* configure.tgt (arm*): Handle NetBSD in the same way as FreeBSD.

libgcc:
	* config.host (arm*-*-netbsdelf*): Add support for EABI configurations.
	* config/arm/t-netbsd (LIB1ASMFUNCS): Add some additional assembler
	functions to build.
	* config/arm/t-netbsd-eabi: New file.

Co-Authored-By: Matthew Green <mrg@eterna.com.au>
Co-Authored-By: Maya Rashish <coypu@sdf.org>
Co-Authored-By: Nick Hudson <skrll@netbsd.org>
Co-Authored-By: Richard Earnshaw <rearnsha@arm.com>
From-SVN: r272290