A more appropriate work around for GHDL is to change the offending call to:
Can you make this change and test it against your current version of GHDL? If you verify that this works in GHDL, I will make the update permanent in the next revision. I have already run regressions with it on the other tools I test with.
P.S. I can send you a beta of 2015.05/2015.06 (not sure when it will be finalized) if you send me an email directly to jim at synthworks.com