env-util: make write_env_file() optionally take headers

This also makes write_env_file() and write_env_file_label() optionally
take dir_fd, and drop write_env_file_at().

Preparation for later commits.

src/shared/env-file-label.c

@@ -6,14 +6,14 @@
 #include "env-file.h"
 #include "selinux-util.h"
 
-int write_env_file_label(const char *fname, char **l) {
+int write_env_file_label(int dir_fd, const char *fname, char **headers, char **l) {
         int r;
 
         r = mac_selinux_create_file_prepare(fname, S_IFREG);
         if (r < 0)
                 return r;
 
-        r = write_env_file(fname, l);
+        r = write_env_file(dir_fd, fname, headers, l);
 
         mac_selinux_create_file_clear();
 

src/shared/env-file-label.h

@@ -5,4 +5,4 @@
  * optimize linking: This way, -lselinux is needed only for the callers of these functions that need selinux, but not
  * for all */
 
-int write_env_file_label(const char *fname, char **l);
+int write_env_file_label(int dir_fd, const char *fname, char **headers, char **l);

src/shared/locale-setup.c

@@ -208,7 +208,7 @@ int locale_context_save(LocaleContext *c, char ***ret_set, char ***ret_unset) {
                 return 0;
         }
 
-        r = write_env_file_label("/etc/locale.conf", set);
+        r = write_env_file_label(AT_FDCWD, "/etc/locale.conf", NULL, set);
         if (r < 0)
                 return r;