Add clean as an argument for cleaning build dir

nob.c

@@ -92,12 +92,42 @@ bool check_kernel(Nob_Cmd *cmd) {
     return true;
 }
 
-bool clean_build() {
+bool clean_dir(const char *dir_path) {
+    Nob_File_Paths children = {0};
+    if (!nob_read_entire_dir(dir_path, &children))
+        return false;
+
+    bool ok = true;
+    for (size_t i = 0; i < children.count; ++i) {
+        const char *name = children.items[i];
+
+        if (strcmp(name, ".") == 0 || strcmp(name, "..") == 0)
+            continue;
+
+        const char *full_path = nob_temp_sprintf("%s/%s", dir_path, name);
+        if (!nob_delete_file(full_path)) {
+            nob_log(NOB_ERROR, "could not delete %s", full_path);
+            ok = false;
+        }
+    }
+
+    nob_da_free(children);
+    return ok;
 }
 
 int main(int argc, char **argv) {
     NOB_GO_REBUILD_URSELF(argc, argv);
 
+    if (argc >= 2) {
+        if (strcmp(argv[1], "clean") == 0) {
+            if (!clean_dir(BUILD_FOLDER))
+                return 1;
+        } else {
+            nob_log(NOB_INFO, "Usage: %s (clean)", argv[0]);
+            return 1;
+        }
+    }
+
     if (!nob_mkdir_if_not_exists(BUILD_FOLDER))
         return 1;