[FastISel][AArch64] Use the proper FMOV instruction to materialize a +0.0.

Use FMOVWSr/FMOVXDr instead of FMOVSr/FMOVDr, which have the proper register
class to be used with the zero register. This makes the MachineInstruction
verifier happy again.

This is related to <rdar://problem/18027157>.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216040 91177308-0d34-0410-b5e6-96231b3b80d8
[dfsan] Treat vararg custom functions like unimplemented functions.

Because declarations of these functions can appear in places like autoconf
checks, they have to be handled somehow, even though we do not support
vararg custom functions. We do so by printing a warning and calling the
uninstrumented function, as we do for unimplemented functions.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@216042 91177308-0d34-0410-b5e6-96231b3b80d8