Fix segfault when code_llvm or code_native are called on a C function

Code that segfaults on current master includes any of the following, and other similar things:
~~~
 code_llvm(match,(Regex,String))
 code_native(match,(Regex,String))
 code_llvm(*,(Array{Int}, Array{Int}))
 code_native(*,(Array{Int}, Array{Int}))
~~~