I tried installing using gem install nmatrix on osx, using gcc 5.2.0.
In file included from nmatrix.cpp:283:0:
[some warnings ...]
/var/folders/sc/2zd_v0qn76gdq5sdg63_jx4r0000gn/T//cc1KmZTQ.s:13579:suffix or operands invalid for `movq'
make: *** [nmatrix.o] Error 1
make failed, exit code 2
I tried to look at cc1KmZTQ.s, but this file doesn't exist after the error.