refactor(lang): reduce scope of HAVE_WORKING_LIBINTL #ifdefs

A lot of code inside HAVE_WORKING_LIBINTL doesn't really depend on a
"working libintl". For instance ex_language is also used for ":lang collate"
and ":lang time".

Also ":lang C" should not fail just because translations aren't available (it
just means use the default text).

References:

https://github.com/neovim/neovim/pull/1 2d00ead2e5
separate ifdefs for locale and gettext got merged together.

8253e29971
Unmotivated switcharoo of get_mess_env() logic. If available, get_locale_val(LC_MESSAGES) is the correct implementation.

src/nvim/cmdexpand.c

@@ -2130,10 +2130,9 @@ static const char *set_context_by_cmdname(const char *cmd, cmdidx_T cmdidx, expa
     set_context_in_runtime_cmd(xp, arg);
     break;
 
-#ifdef HAVE_WORKING_LIBINTL
   case CMD_language:
     return set_context_in_lang_cmd(xp, arg);
-#endif
+
   case CMD_profile:
     set_context_in_profile_cmd(xp, arg);
     break;
@@ -2644,10 +2643,8 @@ static int ExpandOther(char *pat, expand_T *xp, regmatch_T *rmp, char ***matches
     { EXPAND_AUGROUP, expand_get_augroup_name, true, false },
     { EXPAND_SIGN, get_sign_name, true, true },
     { EXPAND_PROFILE, get_profile_name, true, true },
-#ifdef HAVE_WORKING_LIBINTL
     { EXPAND_LANGUAGE, get_lang_arg, true, false },
     { EXPAND_LOCALES, get_locales, true, false },
-#endif
     { EXPAND_ENV_VARS, get_env_name, true, true },
     { EXPAND_USER, get_users, true, false },
     { EXPAND_ARGLIST, get_arglist_name, true, false },

src/nvim/ex_docmd.c

@@ -150,10 +150,6 @@ struct dbg_stuff {
 # include "ex_docmd.c.generated.h"
 #endif
 
-#ifndef HAVE_WORKING_LIBINTL
-# define ex_language            ex_ni
-#endif
-
 // Declare cmdnames[].
 #ifdef INCLUDE_GENERATED_DECLARATIONS
 # include "ex_cmds_defs.generated.h"

src/nvim/gettext.h

@@ -17,7 +17,7 @@
 #  undef setlocale
 # endif
 #else
-# define _(x) (x)
+# define _(x) ((char *)(x))
 # define N_(x) x
 # define NGETTEXT(x, xs, n) ((n) == 1 ? (x) : (xs))
 # define bindtextdomain(x, y)  // empty

src/nvim/os/lang.c

@@ -71,14 +71,17 @@ char *get_mess_lang(void)
   return is_valid_mess_lang(p) ? p : NULL;
 }
 
-// Complicated #if; matches with where get_mess_env() is used below.
-#ifdef HAVE_WORKING_LIBINTL
 /// Get the language used for messages from the environment.
+///
+/// This uses LC_MESSAGES when available, which it is for most systems we build for
+/// except for windows. Then fallback to get the value from the envirionment
+/// ourselves, and use LC_CTYPE as a last resort.
 static char *get_mess_env(void)
 {
-  char *p;
-
-  p = (char *)os_getenv("LC_ALL");
+#ifdef LC_MESSAGES
+  return get_locale_val(LC_MESSAGES);
+#else
+  char *p = (char *)os_getenv("LC_ALL");
   if (p == NULL) {
     p = (char *)os_getenv("LC_MESSAGES");
     if (p == NULL) {
@@ -92,8 +95,8 @@ static char *get_mess_env(void)
     }
   }
   return p;
-}
 #endif
+}
 
 /// Set the "v:lang" variable according to the current locale setting.
 /// Also do "v:lc_time"and "v:ctype".
@@ -104,16 +107,7 @@ void set_lang_var(void)
   loc = get_locale_val(LC_CTYPE);
   set_vim_var_string(VV_CTYPE, loc, -1);
 
-  // When LC_MESSAGES isn't defined use the value from $LC_MESSAGES, fall
-  // back to LC_CTYPE if it's empty.
-#ifdef HAVE_WORKING_LIBINTL
   loc = get_mess_env();
-#elif defined(LC_MESSAGES)
-  loc = get_locale_val(LC_MESSAGES);
-#else
-  // In Windows LC_MESSAGES is not defined fallback to LC_CTYPE
-  loc = get_locale_val(LC_CTYPE);
-#endif
   set_vim_var_string(VV_LANG, loc, -1);
 
   loc = get_locale_val(LC_TIME);
@@ -145,8 +139,6 @@ void init_locale(void)
   TIME_MSG("locale set");
 }
 
-#ifdef HAVE_WORKING_LIBINTL
-
 /// ":language":  Set the language (locale).
 ///
 /// @param eap
@@ -348,8 +340,6 @@ char *get_locales(expand_T *xp, int idx)
   return locales[idx];
 }
 
-#endif
-
 void lang_init(void)
 {
 #ifdef __APPLE__