Fix crash when using the built-in regexp syntax

Fix crash when using the built-in regexp syntax

When /someregexp/ appears in the source, we generate a new regexp
object in the MASM back-end at run-time. That object is memory
managed but it's never marked, because we only store its address
in the generated code.

This patch adds a way for the code generator to collect values that
are generated like this and encoded only in the code directly, and
therefore require extra book-keeping when collecting the roots.

Change-Id: Ia4cc3f4578e2e7e4378ea7ab1a32c66f0e6ab4bf
Reviewed-by: Lars Knoll <lars.knoll@digia.com>