Llvm_bitwriter

`sig
external write_bitcode_file : Llvm.llmodule -> string -> bool
= "llvm_write_bitcode_file"
external write_bitcode_to_fd :
?unbuffered:bool -> Llvm.llmodule -> Unix.file_descr -> bool
= "llvm_write_bitcode_to_fd"
external write_bitcode_to_memory_buffer :
Llvm.llmodule -> Llvm.llmemorybuffer
= "llvm_write_bitcode_to_memory_buffer"
val output_bitcode :
?unbuffered:bool -> Stdlib.out_channel -> Llvm.llmodule -> bool
end`