fixes: improve login environment handling (#114)

* chore(organization): allow nested header and c files

* feat: add shell login "middleware" & etc:
  * lidm now calls `bash` (or other shells, depends on PACKAGE cfg) in
  login mode as a session wrapper to source most env (can be disabled)
  * this fixes a lot of env problems with all `/etc/profile` and more

Extra:
* implemented a musl compatible version of `execvpe` and now lidm should
  search for PATH everywhere it needs to
* `search_path` now also checks if the found binary is properly
  executable
* lidm now uses `confstr` for a decent PATH default if none is found
* logs are unbuffered for cases where debug logs appear empty (exit
  without handlers moment)

* chore: one-time evaluate certain makefile vars

---------

Co-authored-by: grialion <48643945+grialion@users.noreply.github.com>

include/sessions.h

@@ -4,9 +4,8 @@
 #include <sys/types.h>
 #include <unistd.h>
 
-#include "desktop_exec.h"
 #include "macros.h"
-#include "util.h"
+#include "util/vec.h"
 
 enum SessionType {
   XORG,
@@ -51,18 +50,6 @@ static inline struct session_exec session_exec_desktop(
   };
 }
 
-static inline int session_exec_exec(struct session_exec* NNULLABLE exec,
-                                    char* NULLABLE* NNULLABLE envlist) {
-  switch (exec->typ) {
-    case EXEC_SHELL:
-      return execle(exec->shell, exec->shell, NULL, envlist);
-    case EXEC_DESKTOP:
-      return execvpe_desktop(exec->desktop.args, envlist);
-    default:
-      __builtin_unreachable();
-  }
-}
-
 struct session {
   char* NNULLABLE name;
   struct session_exec exec;
@@ -70,5 +57,9 @@ struct session {
 };
 
 struct Vector get_avaliable_sessions();
+int session_exec_exec(struct session_exec* NNULLABLE exec,
+                      char* NULLABLE* NNULLABLE envp);
+int session_exec_login_through_shell(struct session_exec* NNULLABLE exec,
+                                     char* NULLABLE* NNULLABLE envp);
 
 #endif