Dune log with -custom

Workspace root: /Users/corwin/var/tut/dune
Running[0]: /usr/bin/getconf _NPROCESSORS_ONLN > /var/folders/tz/ywq0c4d920n6lkpsgyggj25m0000gn/T/dune72a639.output 2> /dev/null
Auto-detected concurrency: 4
disable binary cache
Running[1]: /opt/local/bin/opam --version --color=never > /var/folders/tz/ywq0c4d920n6lkpsgyggj25m0000gn/T/dunee9b97a.output
Running[2]: /opt/local/bin/opam config env --switch default --sexp --set-switch > /var/folders/tz/ywq0c4d920n6lkpsgyggj25m0000gn/T/dune1af7ea.output
Running[3]: /opt/local/bin/ocamlc.opt -config > /var/folders/tz/ywq0c4d920n6lkpsgyggj25m0000gn/T/dunea3aa3c.output
Dune context:
 { name = "default"
 ; kind = { root = None; switch = "default" }
 ; profile = Release
 ; merlin = true
 ; for_host = None
 ; fdo_target_exe = None
 ; build_dir = "default"
 ; toplevel_path = Some External "/Users/corwin/.opam/default/lib/toplevel"
 ; ocaml_bin = External "/opt/local/bin"
 ; ocaml = Ok External "/Users/corwin/.opam/default/bin/ocaml"
 ; ocamlc = External "/opt/local/bin/ocamlc.opt"
 ; ocamlopt = Ok External "/opt/local/bin/ocamlopt.opt"
 ; ocamldep = Ok External "/opt/local/bin/ocamldep.opt"
 ; ocamlmklib = Ok External "/opt/local/bin/ocamlmklib.opt"
 ; env =
     map
       { "INSIDE_DUNE" : "/Users/corwin/var/tut/dune/_build/default"
       ; "MANPATH" : "/Users/corwin/var/tut/dune/_build/install/default/bin"
       ; "OCAMLFIND_IGNORE_DUPS_IN" :
           "/Users/corwin/var/tut/dune/_build/install/default/lib"
       ; "OCAMLPATH" :
           "/Users/corwin/var/tut/dune/_build/install/default/lib"
       ; "OPAMSWITCH" : "default"
       }
 ; findlib_path = [ External "/Users/corwin/.opam/default/lib" ]
 ; arch_sixtyfour = true
 ; natdynlink_supported = true
 ; supports_shared_libraries = true
 ; ocaml_config =
     { version = "4.08.1"
     ; standard_library_default = "/opt/local/lib/ocaml"
     ; standard_library = "/opt/local/lib/ocaml"
     ; standard_runtime = "the_standard_runtime_variable_was_deleted"
     ; ccomp_type = "cc"
     ; c_compiler = "/usr/bin/clang"
     ; ocamlc_cflags =
         [ "-arch"; "x86_64"; "-O2"; "-fno-strict-aliasing"; "-fwrapv" ]
     ; ocamlopt_cflags =
         [ "-arch"; "x86_64"; "-O2"; "-fno-strict-aliasing"; "-fwrapv" ]
     ; bytecomp_c_compiler =
         [ "/usr/bin/clang"
         ; "-arch"
         ; "x86_64"
         ; "-O2"
         ; "-fno-strict-aliasing"
         ; "-fwrapv"
         ; "-D_FILE_OFFSET_BITS=64"
         ; "-D_REENTRANT"
         ]
     ; bytecomp_c_libraries = [ "-lm"; "-lpthread" ]
     ; native_c_compiler =
         [ "/usr/bin/clang"
         ; "-arch"
         ; "x86_64"
         ; "-O2"
         ; "-fno-strict-aliasing"
         ; "-fwrapv"
         ; "-D_FILE_OFFSET_BITS=64"
         ; "-D_REENTRANT"
         ]
     ; native_c_libraries = [ "-lm" ]
     ; cc_profile = [ "-pg" ]
     ; architecture = "amd64"
     ; model = "default"
     ; int_size = 63
     ; word_size = 64
     ; system = "macosx"
     ; asm = [ "/usr/bin/clang"; "-arch"; "x86_64"; "-Wno-trigraphs"; "-c" ]
     ; asm_cfi_supported = true
     ; with_frame_pointers = false
     ; ext_exe = ""
     ; ext_obj = ".o"
     ; ext_asm = ".s"
     ; ext_lib = ".a"
     ; ext_dll = ".so"
     ; os_type = "Unix"
     ; default_executable_name = "a.out"
     ; systhread_supported = true
     ; host = "x86_64-apple-darwin19.2.0"
     ; target = "x86_64-apple-darwin19.2.0"
     ; profiling = true
     ; flambda = false
     ; spacetime = false
     ; safe_string = false
     ; exec_magic_number = "Caml1999X025"
     ; cmi_magic_number = "Caml1999I025"
     ; cmo_magic_number = "Caml1999O025"
     ; cma_magic_number = "Caml1999A025"
     ; cmx_magic_number = "Caml1999Y025"
     ; cmxa_magic_number = "Caml1999Z025"
     ; ast_impl_magic_number = "Caml1999M025"
     ; ast_intf_magic_number = "Caml1999N025"
     ; cmxs_magic_number = "Caml1999D025"
     ; cmt_magic_number = "Caml1999T025"
     ; natdynlink_supported = true
     ; supports_shared_libraries = true
     ; windows_unicode = false
     }
 }
Actual targets:
- _build/default/a.bc