Alter constant-flow memsan testing

Disable asm in memsan constant-flow testing and add a check in
check_config.h

Signed-off-by: Elena Uziunaite <elena.uziunaite@arm.com>
diff --git a/include/mbedtls/check_config.h b/include/mbedtls/check_config.h
index 67a05f8..a17ccb8 100644
--- a/include/mbedtls/check_config.h
+++ b/include/mbedtls/check_config.h
@@ -247,6 +247,9 @@
 #if defined(MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN) &&  !defined(MBEDTLS_HAS_MEMSAN)
 #error "MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN requires building with MemorySanitizer"
 #endif
+#if defined(MBEDTLS_HAS_MEMSAN) && defined(MBEDTLS_HAVE_ASM)
+#error "MEMSAN does not support assembly implementation"
+#endif
 #undef MBEDTLS_HAS_MEMSAN // temporary macro defined above
 
 #if defined(MBEDTLS_CCM_C) && \