[WebAssembly] Create section start symbols automatically for all sections

These symbols only get included in the output symbols table if
they are used in a relocation.

This behaviour matches more closely the ELF object writer.

Differential Revision: https://reviews.llvm.org/D46561

llvm-svn: 332005
diff --git a/llvm/lib/MC/MCWasmStreamer.cpp b/llvm/lib/MC/MCWasmStreamer.cpp
index 153ea25..984f491 100644
--- a/llvm/lib/MC/MCWasmStreamer.cpp
+++ b/llvm/lib/MC/MCWasmStreamer.cpp
@@ -66,6 +66,7 @@
     Asm.registerSymbol(*Grp);
 
   this->MCObjectStreamer::ChangeSection(Section, Subsection);
+  Asm.registerSymbol(*Section->getBeginSymbol());
 }
 
 void MCWasmStreamer::EmitWeakReference(MCSymbol *Alias,