test-lib: ignore leaks in the sanitizer's thread code

Our CI jobs sometimes see false positive leaks like this:

        =================================================================
        ==3904583==ERROR: LeakSanitizer: detected memory leaks

        Direct leak of 32 byte(s) in 1 object(s) allocated from:
            #0 0x7fa790d01986 in __interceptor_realloc ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:98
            #1 0x7fa790add769 in __pthread_getattr_np nptl/pthread_getattr_np.c:180
            #2 0x7fa790d117c5 in __sanitizer::GetThreadStackTopAndBottom(bool, unsigned long*, unsigned long*) ../../../../src/libsanitizer/sanitizer_common/sanitizer_linux_libcdep.cpp:150
            #3 0x7fa790d11957 in __sanitizer::GetThreadStackAndTls(bool, unsigned long*, unsigned long*, unsigned long*, unsigned long*) ../../../../src/libsanitizer/sanitizer_common/sanitizer_linux_libcdep.cpp:598
            #4 0x7fa790d03fe8 in __lsan::ThreadStart(unsigned int, unsigned long long, __sanitizer::ThreadType) ../../../../src/libsanitizer/lsan/lsan_posix.cpp:51
            #5 0x7fa790d013fd in __lsan_thread_start_func ../../../../src/libsanitizer/lsan/lsan_interceptors.cpp:440
            #6 0x7fa790adc3eb in start_thread nptl/pthread_create.c:444
            #7 0x7fa790b5ca5b in clone3 ../sysdeps/unix/sysv/linux/x86_64/clone3.S:81

This is not a leak in our code, but appears to be a race between one
thread calling exit() while another one is in LSan's stack setup code.
You can reproduce it easily by running t0003 or t5309 with --stress
(these trigger it because of the threading in git-grep and index-pack
respectively).

This may be a bug in LSan, but regardless of whether it is eventually
fixed, it is useful to work around it so that we stop seeing these false
positives.

We can recognize it by the mention of the sanitizer functions in the
DEDUP_TOKEN line. With this patch, the scripts mentioned above should
run with --stress indefinitely.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/test-lib.sh

@@ -1177,7 +1177,8 @@ check_test_results_san_file_empty_ () {
 	! find "$TEST_RESULTS_SAN_DIR" \
 		-type f \
 		-name "$TEST_RESULTS_SAN_FILE_PFX.*" 2>/dev/null |
-	xargs grep -q ^DEDUP_TOKEN
+	xargs grep ^DEDUP_TOKEN |
+	grep -qv sanitizer::GetThreadStackTopAndBottom
 }
 
 check_test_results_san_file_ () {