testsuite, asan: Avoid color in asan test output.

The presence of the color markers in the some of the asan tests
appears to confuse the dg-output matching (possibly a platform
TCL or termios bug) on some Darwin platforms.

Since the color is not being tested, switch it off (makes the log
files easier to read too).  This fixes a large number of spurious
test fails on AVX512 Darwin19.

Signed-off-by: Iain Sandoe <iain@sandoe.co.uk>

gcc/testsuite/ChangeLog:

	* lib/asan-dg.exp: Do not apply color to asan output when
	under test.

gcc/testsuite/lib/asan-dg.exp

@@ -111,6 +111,8 @@ proc asan_init { args } {
     global asan_saved_TEST_ALWAYS_FLAGS
     global asan_saved_ALWAYS_CXXFLAGS
 
+    setenv ASAN_OPTIONS "color=never"
+
     set link_flags ""
     if ![is_remote host] {
 	if [info exists TOOL_OPTIONS] {