MAGIC_MODULE and libc

I just upgraded to v8.2 and have an issue with one of my stored
proc/functions that worked under 8.1:

CREATE OR REPLACE FUNCTION getpid()
RETURNS integer AS
'/lib/libc.so.6', 'getpid'
LANGUAGE 'c' VOLATILE;

ERROR: incompatible library "/lib/libc.so.6": missing magic block
SQL state: XX000
Hint: Extension libraries are required to use the PG_MODULE_MAGIC macro.

I've added the appropriate macro to all my actual C code...but in this
case surely I am not expected to recompile libc...am I? Is there an
easier way to get the pid of the current process?