Delay creating an alias for @@@.

With this we only create an alias for @@@ once we know if it should
use @ or @@. This avoids last minutes renames and hacks to handle MS
names.

This only handles the ELF writer. LTO still has issues with @@@
aliases.

llvm-svn: 327160
diff --git a/llvm/lib/MC/MCStreamer.cpp b/llvm/lib/MC/MCStreamer.cpp
index bf27a0a..7d847c6 100644
--- a/llvm/lib/MC/MCStreamer.cpp
+++ b/llvm/lib/MC/MCStreamer.cpp
@@ -929,7 +929,7 @@
   llvm_unreachable("this directive only supported on COFF targets");
 }
 void MCStreamer::emitELFSize(MCSymbol *Symbol, const MCExpr *Value) {}
-void MCStreamer::emitELFSymverDirective(MCSymbol *Alias,
+void MCStreamer::emitELFSymverDirective(StringRef AliasName,
                                         const MCSymbol *Aliasee) {}
 void MCStreamer::EmitLocalCommonSymbol(MCSymbol *Symbol, uint64_t Size,
                                        unsigned ByteAlignment) {}