Many thanks to everyone who has helped me on this issue.
I ended up abandoning the crosstool approach. It supports mips32 well, but
not mips64. Linux from scratch has a very good step by step procedure for
building a tool chain for mips64. I was able to build with very little
headaches. Unfortunately, I have not yet been able to execute any programs
compiled with the tool chain. I'm not sure where I went wrong.
PMC sierra is working on an update for their tool chain. They have supplied
me with a "beta" version tool chain that has solved my problems. Now, I am
able to compile with -mabi=64 and -lpthread. The executable no longer
Segfaults. Since I'm past this problem, I will probably not spend much more
time trying to build a working tool chain.