Revert "Lose the hand-written futex assembler."

This reverts commit ced906c849704f379d7191822f6d74993d4fa296.

Causes issues on art / dalvik due to a broken return value
check and other undiagnosed issues.

bug: 15195455

Change-Id: I5d6bbb389ecefb0e33a5237421a9d56d32a9317c
diff --git a/libc/SYSCALLS.TXT b/libc/SYSCALLS.TXT
index 785d191..60cf980 100644
--- a/libc/SYSCALLS.TXT
+++ b/libc/SYSCALLS.TXT
@@ -305,6 +305,8 @@
 void _exit|_Exit:exit_group(int)  all
 void __exit:exit(int)  all
 
+int futex(void*, int, int, void*, void*, int)  all
+
 int inotify_init1(int)  all
 int inotify_add_watch(int, const char*, unsigned int)  all
 int inotify_rm_watch(int, unsigned int)  all