Fix calls to varargs C function fcntl
The ccall calling convention doesn't support varargs functions, so switch to capi instead. See https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/ffi.html#varargs-not-supported-by-ccall-calling-convention
The ccall calling convention doesn't support varargs functions, so switch to capi instead. See https://ghc.gitlab.haskell.org/ghc/doc/users_guide/exts/ffi.html#varargs-not-supported-by-ccall-calling-convention