Inlining intrinsics across crates causes link errors

[eholk]

I will commit a test case shortly. Here is the error message:

note: Undefined symbols for architecture x86_64:
  "rusti::atomic_xchng::_90ba6d45f3724239::_00", referenced from:
      main::_4d18ee73dd908dc4::_00      in intrinsic-atomics-cc.o
      __rust_main in intrinsic-atomics-cc.o
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status

@nikomatsakis thinks this could be because attributes (and thus the ABI attribute) are not serialized.

[brson]

Fixed by ac31fdd