[PATCH, v2, rs6000] pr65479 Add -fasynchronous-unwind-tables when the -fsanitize=address option is seen.

All feedback from the earlier version has been taken into account now.

This patch adds the -fasynchronous-unwind-tables option to compilations when
the -fsanitize=address option is seen but not if any
-fasynchronous-unwind-tables options were already specified.
-fasynchronous-unwind-tables causes a full strack trace to be produced when
the sanitizer detects an error.  Without the full trace several of the asan
test cases fail on powerpc.

See https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65479 for more information.

Bootstrapped and tested on powerpc64le-unknown-linux-gnu,
powerpc64be-unknown-linux-gnu, and x86_64-pc-linux-gnu with no regressions.
Is this ok for trunk?

[gcc]

2016-12-21  Bill Seurer  <seurer@linux.vnet.ibm.com>

	PR sanitizer/65479
	* config/rs6000/rs6000.c (rs6000_option_override_internal): Add
	-fasynchronous-unwind-tables option when -fsanitize=address is
	specified.

From-SVN: r243863