-lpthread missing in LDLIBS

[rok-cesnovar]

Thanks Sean for this repository, love it!

Just a minor observation, on Ubuntu I had to add -lpthread to LDLIBS to compile the matstuff example.

Otherwise I got
benchmark.cc:(.text+0x2a57): undefined reference to pthread_create'`

[seantalts]

Ah yeah, I need to figure out if I can just import more of the Math library makefiles to handle stuff like that...