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/arch-arm64/arm64.mk b/libc/arch-arm64/arm64.mk
index 93b0b0b..7a9eb4e 100644
--- a/libc/arch-arm64/arm64.mk
+++ b/libc/arch-arm64/arm64.mk
@@ -37,6 +37,7 @@
     arch-arm64/bionic/__bionic_clone.S \
     arch-arm64/bionic/bzero_arm64.c \
     arch-arm64/bionic/_exit_with_stack_teardown.S \
+    arch-arm64/bionic/futex_arm64.S \
     arch-arm64/bionic/__get_sp.S \
     arch-arm64/bionic/__rt_sigreturn.S \
     arch-arm64/bionic/_setjmp.S \