add -lgthread-2.0 to LDFLAGS on NetBSD, as is already done for SunOS and
DragonFly:

ld: evolution-webcal-main.o: undefined reference to symbol 'g_thread_init'
ld: note: 'g_thread_init' is defined in DSO /usr/pkg/lib/libgthread-2.0.so.0 so try adding it to the linker command line
/usr/pkg/lib/libgthread-2.0.so.0: could not read symbols: Invalid operation

(jmcneill)