Fails to compile with --target=asmjs-unknown-emscripten

[LukasKalbertodt]

When compiling with the newest nightly compiler and cargo build --target=asmjs-unknown-emscripten, this happens:

   Compiling num_cpus v1.1.0 (file:///path/to/num_cpus)
error[E0425]: unresolved name `get_num_cpus`
  --> src/lib.rs:12:5
   |
12 |     get_num_cpus()
   |     ^^^^^^^^^^^^ unresolved name

error[E0425]: unresolved name `get_num_cpus`
  --> src/lib.rs:28:5
   |
28 |     get_num_cpus()
   |     ^^^^^^^^^^^^ unresolved name