Revert "Remove the return type from the syscall lists and parser."

This reverts commit 83f08aa3c6aaaa810319e7068c1bb3f63bfdb6a0.

Reason for revert: DroidMonitor: Potential culprit for b/395697512 - verifying through ABTD before revert submission. This is part of the standard investigation process, and does not mean your CL will be reverted.

Change-Id: I891cb76071b5745743676eada6154302cc3f5dae
diff --git a/libc/SECCOMP_BLOCKLIST_COMMON.TXT b/libc/SECCOMP_BLOCKLIST_COMMON.TXT
index 0c6e1ae..22c9844 100644
--- a/libc/SECCOMP_BLOCKLIST_COMMON.TXT
+++ b/libc/SECCOMP_BLOCKLIST_COMMON.TXT
@@ -6,5 +6,5 @@
 #
 # This file is processed by a python script named genseccomp.py.
 
-swapon(const char*, int) all
-swapoff(const char*) all
+int     swapon(const char*, int) all
+int     swapoff(const char*) all