Add configure flags to for 32-bit build on 64-bit Mac OS X machine

I tried and found that configure fails on 64-bit Mac OS X machine with no configure flags.
Following https://github.com/Aries85/LightZone/commit/4e376e, I added "-m32" to CFLAGS and LDFLAGS and it builds successfully.

Could you review this pull request and merge it?
Thanks!