[MC] Factor MCObjectStreamer::addFragmentAtoms out of MachO streamer.

This code previously existed only in MCMachOStreamer but is
useful for WebAssembly too.  See: D46335

Differential Revision: https://reviews.llvm.org/D46297

llvm-svn: 331412
diff --git a/llvm/lib/MC/MCWasmStreamer.cpp b/llvm/lib/MC/MCWasmStreamer.cpp
index 2c77624..504c72c 100644
--- a/llvm/lib/MC/MCWasmStreamer.cpp
+++ b/llvm/lib/MC/MCWasmStreamer.cpp
@@ -198,6 +198,9 @@
 void MCWasmStreamer::FinishImpl() {
   EmitFrames(nullptr);
 
+  // Set fragment atoms so we can map from code fragment to defining symbol
+  addFragmentAtoms();
+
   this->MCObjectStreamer::FinishImpl();
 }