Auto merge of #885 - EdSchouten:nprocessors, r=alexcrichton

Add _SC_NPROCESSORS_ONLN for CloudABI.

This constant is not used by the C library, which is why I didn't add it
initially. It is, however, used by libtest to determine the parallelism
for the execution of tests.

Author: bors

src/cloudabi/mod.rs

@@ -55,6 +55,7 @@ s! {
     }
 }
 
+pub const _SC_NPROCESSORS_ONLN: ::c_int = 52;
 pub const _SC_PAGESIZE: ::c_int = 54;
 
 pub const AF_INET: ::c_int = 1;