Fix common misspellings

Fixes generated by 'codespell' and manually reviewed.

Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
diff --git a/kernel/exit.c b/kernel/exit.c
index 6a488ad..f5d2f63 100644
--- a/kernel/exit.c
+++ b/kernel/exit.c
@@ -841,7 +841,7 @@
 	/* Let father know we died
 	 *
 	 * Thread signals are configurable, but you aren't going to use
-	 * that to send signals to arbitary processes.
+	 * that to send signals to arbitrary processes.
 	 * That stops right now.
 	 *
 	 * If the parent exec id doesn't match the exec id we saved