Detect enabled GCC/Clang sanitizers

Occasionally we want tests to take advantage of sanitizers, or work around
them.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>

tests/include/test/helpers.h

@@ -19,6 +19,21 @@
 #include MBEDTLS_CONFIG_FILE
 #endif
 
+#if defined(__SANITIZE_ADDRESS__) /* gcc -fsanitize=address */
+#  define MBEDTLS_TEST_HAVE_ASAN
+#endif
+#if defined(__has_feature)
+#  if __has_feature(address_sanitizer) /* clang -fsanitize=address */
+#    define MBEDTLS_TEST_HAVE_ASAN
+#  endif
+#  if __has_feature(memory_sanitizer) /* clang -fsanitize=memory */
+#    define MBEDTLS_TEST_HAVE_MSAN
+#  endif
+#  if __has_feature(thread_sanitizer) /* clang -fsanitize=thread */
+#    define MBEDTLS_TEST_HAVE_TSAN
+#  endif
+#endif
+
 #if defined(MBEDTLS_THREADING_C) && defined(MBEDTLS_THREADING_PTHREAD) && \
     defined(MBEDTLS_TEST_HOOKS)
 #define MBEDTLS_TEST_MUTEX_USAGE