[LAD] LADSPA plugin undefined symbols

(Hope this is the right place to ask - apologies if not). I'm trying to test my new LADSPA plugin with demolition but the latter fails due to undefined symbols. Running objdump -t on the .so lists several of the standard C functions used in the code as undefined symbols. I've tried installing libc6-dbg and adding -g to the CFLAGS in the makefile (which is a modified version of the one in ladspa_sdk) but it makes no difference. System is Debian testing amd64 (pre-multi-arch snapshot from Jan 2012). I thought it might be due to a mismatch in the build tools, so I tried building the plugin on Debian Lenny (5.0.3). The same thing happens there. I've tried running demolition on a couple of the Debian packaged swh-plugins and it runs without a problem, but any plugin I compile from source (not just mine) gives the same type of error. All of the undefined symbols are standard libc functions like malloc, calloc, free, cos etc. The plugin works perfectly in Ardour2 on both systems. Anyone have any ideas how to fix this? John