Rename and slightly modify ocamlobjinfo's -no-crc command-line option

Instead of printing no CRC at all, this option should rather preserve the
distinction between no CRC at all (represented by a dummy CRC
consisting of 32 '-' characters) and a real CRC represented by a
null CRC consisting of 32 '0' characters.

This commit thus renames the option from -no-crc to -null-crc.

Changes

@@ -249,7 +249,7 @@ Working version
   boot/ocamlc -depend can be used in its place.
   (Nicolás Ojeda Bär, review by Xavier Leroy and Damien Doligez)
 
-- GPR#1695: add the -no-crc command-line option to ocamlobjinfo.
+- GPR#1695: add the -null-crc command-line option to ocamlobjinfo.
   (Sébastien Hinderer, review by David Allsopp and Gabriel Scherer)
 
 ### Manual and documentation:

tools/objinfo.ml

@@ -44,14 +44,14 @@ let input_stringlist ic len =
   get_string_list sect len
 
 let dummy_crc = String.make 32 '-'
+let null_crc = String.make 32 '0'
 
 let print_name_crc (name, crco) =
   let crc =
-    if !no_crc then "" else begin
-      match crco with
-        None -> dummy_crc
-      | Some crc -> Digest.to_hex crc
-    end
+    match crco with
+      None -> dummy_crc
+    | Some crc ->
+      if !no_crc then null_crc else Digest.to_hex crc
   in
     printf "\t%s\t%s\n" crc name
 
@@ -328,7 +328,7 @@ let dump_obj filename =
 let arg_list = [
   "-no-approx", Arg.Set no_approx, " Do not print module approximation information";
   "-no-code", Arg.Set no_code, " Do not print code from exported flambda functions";
-  "-no-crc", Arg.Set no_crc, " Do not print the CRC of imported interfaces";
+  "-null-crc", Arg.Set no_crc, " Print a null CRC for imported interfaces";
   "-args", Arg.Expand Arg.read_arg,
      "<file> Read additional newline separated command line arguments \n\
      \      from <file>";