Replaces vfork() implementation with fork()

vfork() was removed from POSIX 2008, so this replaces its implementation
with a call to fork().

Bug: 13935372
Change-Id: I6d99ac9e52a2efc5ee9bda1cab908774b830cedc
diff --git a/libc/Android.mk b/libc/Android.mk
index ee8981a..3512771 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -224,6 +224,7 @@
     bionic/umount.cpp \
     bionic/unlink.cpp \
     bionic/utimes.cpp \
+    bionic/vfork.cpp \
     bionic/wait.cpp \
     bionic/wchar.cpp \
     bionic/wctype.cpp \