bnlearn package compilation failure on MacOSX

Hi all.

I've recently uploaded a package (bnlearn) to CRAN. It builds fine 
on both Linux (32 and 64 bit) and Windows, but fails on MacOSX ix86
because of C90 vs C99 issues:

http://www.r-project.org/nosvn/R.check/r-patched-macosx-ix86/bnlearn-00install.html

Since I've no MacOSX machine at hand, I would like to ask you:
why is C99 not the default for gcc on MacOSX ix86? Is it safe to 
force gcc to use C99 with either -std=c99 o -std=gnu99?

Thanks in advance.

Marco Scutari                               
Linux Registered User #341807                  http://counter.li.org
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