Add option to test constant-flow with valgrind

Currently the new component in all.sh fails because
mbedtls_ssl_cf_memcpy_offset() is not actually constant flow - this is on
purpose to be able to verify that the new test works.

Signed-off-by: Manuel Pégourié-Gonnard <manuel.pegourie-gonnard@arm.com>
diff --git a/programs/test/query_config.c b/programs/test/query_config.c
index 23dc515..c242ab5 100644
--- a/programs/test/query_config.c
+++ b/programs/test/query_config.c
@@ -1546,6 +1546,14 @@
     }
 #endif /* MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN */
 
+#if defined(MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND)
+    if( strcmp( "MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND", config ) == 0 )
+    {
+        MACRO_EXPANSION_TO_STR( MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND );
+        return( 0 );
+    }
+#endif /* MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND */
+
 #if defined(MBEDTLS_TEST_HOOKS)
     if( strcmp( "MBEDTLS_TEST_HOOKS", config ) == 0 )
     {