Deduplicate errno values in errno2name()

On Darwin, the EQFULL and ELAST error constants lead to the same errno
value (106), so we get a build error like this:

  src/errno_list.cc:228:14: error: duplicate case value '106'
        case 106: return "EQFULL";
             ^
  src/errno_list.cc:227:14: note: previous case defined here
        case 106: return "ELAST";
             ^

We can simply throw away the duplicate values, because all that
errno2name is used for is printing the current rules with the -p command
line argument.

Signed-off-by: aszlig <aszlig@nix.build>

Author: aszlig

scripts/generrno.py

@@ -33,7 +33,7 @@
 
 out += 'const std::string errno2name(int num)\n{\n'
 out += '    switch (num) {\n'
-for number, name in errnos:
+for number, name in dict(errnos).items():
     out += '        case ' + str(number) + ': return "' + name + '";\n'
 out += '        default: return "<unknown>";\n'
 out += '    }\n'