This patch starts simplifying the handling of .symver.
For now it just moves the responsibility for creating an alias down to
the streamer. With that the asm streamer can pass a .symver unchanged,
which is nice since gas cannot parse "foo@bar = zed".
In a followup I hope to move the handling down to the writer so that
we don't need special hacks for avoiding breaking names with @@@ on
windows.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@327101 91177308-0d34-0410-b5e6-96231b3b80d8