module CallConv:sig..end
Llvm.function_call_conv and Llvm.set_function_call_conv. Calling
    conventions are open-ended.val c : intc is the C calling convention.val fast : intfast is the calling convention to allow LLVM
                              maximum optimization opportunities. Use only with
                              internal linkage.val cold : intcold is the calling convention for
                              callee-save.val x86_stdcall : intx86_stdcall is the familiar stdcall calling
                              convention from C.val x86_fastcall : intx86_fastcall is the familiar fastcall calling
                              convention from C.