[plt-scheme] passing flags to gcc

I used to be able to pass command line flags to gcc via mzc with the 
++ccf flag (and ++ldf analogously for the liner), but it doesn't seem to 
work anymore.  Here are the relevant parts of compiling a program that 
depends on somefoo.h, found in /local/include/foo, but notice that the 
-I flag is not given as an argument to gcc:

mzc -v --auto-dir ++ccf -I/local/include/foo foo.ss
mzc v371 [3m], Copyright (c) 2004-2007 PLT Scheme Inc.
"foo.ss":
  Reading...  expanding...
  (...... elided .....)
  [xforming C to "/usr/tmp/mzcTMPfoo3m.c"]
xform-cpp: (/usr/bin/gcc -E -DMZ_PRECISE_GC -I/local/include/plt 
-I/local/lib/plt/collects/compiler -DMZ_XFORM -DMZ_PRECISE_GC 
-DGC_STACK_CALLEE_RESTORE /usr/tmp/mzcTMPfoo.c)
/usr/tmp/mzcTMPfoo.c:7:19: error: somefoo.h: No such file or directory


What am I doing wrong?

Thanks,
David