Add support for subsections to the ELF assembler. Fixes PR8717.

Differential Revision: http://llvm-reviews.chandlerc.com/D598

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179725 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCNullStreamer.cpp b/lib/MC/MCNullStreamer.cpp
index c872b22..659706a 100644
--- a/lib/MC/MCNullStreamer.cpp
+++ b/lib/MC/MCNullStreamer.cpp
@@ -30,13 +30,14 @@
     virtual void InitSections() {
     }
 
-    virtual void ChangeSection(const MCSection *Section) {
+    virtual void ChangeSection(const MCSection *Section,
+                               const MCExpr *Subsection) {
     }
 
     virtual void EmitLabel(MCSymbol *Symbol) {
       assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
-      assert(getCurrentSection() && "Cannot emit before setting section!");
-      Symbol->setSection(*getCurrentSection());
+      assert(getCurrentSection().first &&"Cannot emit before setting section!");
+      Symbol->setSection(*getCurrentSection().first);
     }
     virtual void EmitDebugLabel(MCSymbol *Symbol) {
       EmitLabel(Symbol);