This patch changes how to specify ABI and link name of a native module.
Before:
native "cdecl" mod llvm = "rustllvm" {...}
After:
#[abi = "cdecl"]
#[link_name = "rustllvm"]
native mod llvm {...}
The old optional syntax for ABI and link name is no longer supported.
Fixes issue #547
Note: I found a bug in c-stack-cdecl which codes not permit such
native functions to be used as values. I added an xfail-test
(c-stack-as-value) documenting it.
