Another option would be to update the compiler options to add "-std=c89"

That's pretty easy to try out if you think it might help.
The following is a simple technique that I've used many times on Windows ... and I think it would be just as affective on other systems (but I haven't tested that).
In one of your @INC directories, just create a .pm file named (say) AltConfig.pm, which contains (eg):

package AltConfig;
use warnings;
use Config;

my $ccflags = $Config{ccflags};
$ccflags .= ' -std=c89';

my $obj = tied %Config;
$obj->{ccflags} = $ccflags;

1;
[download]

Then set the PERL5OPT environment variable to contain -MAltConfig
That will probably mean that you have to create that environment variable - but I don't rule out the possibility that PER5OPT already exists (in which case you simply add -MAltConfig to it.)
For as long as that environment variable contains that spec, the AltConfig module will be loaded whenever Perl is invoked, and $Config{ccflags} will have the "std=c89" flag appended to it.
You can easily verify this by running perl -V:ccflags

Inside AltConfig.pm you can alter ccflags (or any other %Config key) to specify precisely whatever you want.
Reverting to your original perl setup is then as simple as removing -MAltConfig from the PERL5OPT environment variable.

I don't know if that will prove to be useful in fixing your issue ... but it's simple enough to try out, if you want.

Cheers,
Rob