This is a better solution than the old __warn_references because it's
a compile-time rather than link-time warning, it doesn't rely on something
that doesn't appear to be supported by gold (which is why you only used
to see these warnings on mips builds), and the errors refer to the exact
call site(s) rather than just telling you which object file contains a
reference to the bad function.
This is primarily so we can build bionic for aarch64; building libc.so
caused these warnings to fire (because link time is the wrong time) and
warnings are errors.
Change-Id: I5df9281b2a9d98b164a9b11807ea9472c6faa9e3
c13fb75cea