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/util/vec.h

@@ -0,0 +1,26 @@
+#ifndef UTIL_VEC_H
+#define UTIL_VEC_H
+
+#include <stddef.h>
+#include <stdint.h>
+
+struct Vector {
+  uint32_t length;
+  uint32_t capacity;
+  void** pages;
+};
+
+struct Vector vec_from_raw(void** raw);
+void** vec_as_raw(struct Vector self);
+extern const struct Vector VEC_NEW;
+int vec_resize(struct Vector* self, size_t size);
+int vec_reserve(struct Vector* self, size_t size);
+int vec_reserve_exact(struct Vector* self, size_t size);
+int vec_push(struct Vector* self, void* item);
+void vec_free(struct Vector* self);
+void vec_clear(struct Vector* self);
+void vec_reset(struct Vector* self);
+void* vec_pop(struct Vector* self); // won't free it, nor shrink vec list space
+void* vec_get(struct Vector* self, size_t index);
+
+#endif /* UTIL_VEC_H */