Introduce libsanitizer to GCC tree

Takes the libhwasan library from LLVM and puts it into our source tree
excluding the build system files.

Tieing the source files into our build system is done in a later commit.

We have taken the libsanitizer library from the same SVN revision as
the other sanitizer libraries are taken from (SVN revision 345033 as
mentioned in libsanitizer/MERGE).

libsanitizer/ChangeLog:

2019-09-06  Matthew Malcomson  <matthew.malcomson@arm.com>

	* hwasan/hwasan.cc: New file.
	* hwasan/hwasan.h: New file.
	* hwasan/hwasan.syms.extra: New file.
	* hwasan/hwasan_allocator.cc: New file.
	* hwasan/hwasan_allocator.h: New file.
	* hwasan/hwasan_blacklist.txt: New file.
	* hwasan/hwasan_dynamic_shadow.cc: New file.
	* hwasan/hwasan_dynamic_shadow.h: New file.
	* hwasan/hwasan_flags.h: New file.
	* hwasan/hwasan_flags.inc: New file.
	* hwasan/hwasan_interceptors.cc: New file.
	* hwasan/hwasan_interface_internal.h: New file.
	* hwasan/hwasan_linux.cc: New file.
	* hwasan/hwasan_mapping.h: New file.
	* hwasan/hwasan_new_delete.cc: New file.
	* hwasan/hwasan_poisoning.cc: New file.
	* hwasan/hwasan_poisoning.h: New file.
	* hwasan/hwasan_report.cc: New file.
	* hwasan/hwasan_report.h: New file.
	* hwasan/hwasan_thread.cc: New file.
	* hwasan/hwasan_thread.h: New file.
	* hwasan/hwasan_thread_list.cc: New file.
	* hwasan/hwasan_thread_list.h: New file.