Revert "Replaces vfork() implementation with fork()"

We're getting cold feet on this one... let's put it back.

This reverts commit 210331d9762037afb9b5ed8413079c6f65872df9.

Change-Id: I6b0d3c2b1dbf7f1dc9566979a91b7504c2189269
diff --git a/libc/arch-arm64/arm64.mk b/libc/arch-arm64/arm64.mk
index 314358e..ed991ce 100644
--- a/libc/arch-arm64/arm64.mk
+++ b/libc/arch-arm64/arm64.mk
@@ -36,6 +36,7 @@
     arch-arm64/bionic/__set_tls.c \
     arch-arm64/bionic/sigsetjmp.S \
     arch-arm64/bionic/syscall.S \
+    arch-arm64/bionic/vfork.S \
 
 
 libc_crt_target_cflags_arm64 := \