Fix the Windows native x86-64 build.

	PR driver/78196
	* Makefile.in (SELFTEST_FLAGS): Added -o /dev/null.

From-SVN: r241895

gcc/ChangeLog

+2016-11-07  Tamar Christina  <tamar.christina@arm.com>
+
+	PR driver/78196
+	* Makefile.in (SELFTEST_FLAGS): Added -o /dev/null.
+
 2016-11-07  Martin Liska  <mliska@suse.cz>
 
 	* tree-profile.c (gimple_gen_time_profiler): Set proper type

gcc/Makefile.in

@@ -1879,7 +1879,10 @@ rest.cross: specs
 # Specify a dummy input file to placate the driver.
 # Specify -nostdinc to work around missing WIND_BASE environment variable
 # required for *-wrs-vxworks-* targets.
-SELFTEST_FLAGS = -nostdinc -x c /dev/null -S -fself-test
+# Specify -o /dev/null so the output of -S is discarded. More importantly
+# It does not try to create a file with the name "null.s" on POSIX and
+# "nul.s" on Windows. Because on Windows "nul" is a reserved file name.
+SELFTEST_FLAGS = -nostdinc -x c /dev/null -S -fself-test -o /dev/null
 
 # Run the selftests during the build once we have a driver and a cc1,
 # so that self-test failures are caught as early as possible.