This also means we don't need a separate avrdude.conf for the 64-bit Linux version of avrdude.
(cherry picked from commit 6e227dda6ed63b5c7624e2173a9d334f32e116e6)
Includes changes to the build.xml, 64-bit versions of avrdude and RXTX native libraries, and alternative versions of the RXTX jar and avrdude.conf for those 64-bit versions (because they also have other differences).
(cherry picked from commit 253ab0cacea161c6f558d6a26fb3ed258057656a)