I have a work around so it's not a big deal, but I thought I should report it.

When compiling a loadable library on mac osx 10.3.9 using the following command-line

gcc -bundle -o example-program foo.o _example-program.o -L/usr/local/Gambit-C/lib -lgambc

The result is

ld: Undefined symbols: _environ

The work around is to change the command line options

gcc -bundle -flat_namespace -undefined suppress -o example-program foo.o _example-program.o -L/usr/local/Gambit-C/lib -lgambc

Which compiles just fine, but doesn't quite feel right. After much research I happened across http://wiki.opendarwin.org/index.php/Fink:Porting_Notes#The__environ_symbol which details the actual problem is and how to go about fixing it. I may poke around in the gambit source and see what I can see.