On my system:

  gcc -O3
  1m40.302s

  gcc -O3 -ffast-math
  0m5.110s

  rustc -C opt-level=3
  0m9.278s

gcc (GCC) 6.3.1 20170109

rustc 1.15.1 (021bd294c 2017-02-08)

Edit: Looking into this a bit more, I think 'rustc -C opt-level=3' is optimizing out the actual integration. If I put a println!("{}", x[0][0]) at the end, I end up with 1m43s. Not sure what 'gcc -O3 -ffast-math' is doing; I haven't looked at the disassembly.