Add support for pushsection and popsection. Patch by Joerg Sonnenberger.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@125629 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCNullStreamer.cpp b/lib/MC/MCNullStreamer.cpp
index b9393ff..08ddf01 100644
--- a/lib/MC/MCNullStreamer.cpp
+++ b/lib/MC/MCNullStreamer.cpp
@@ -28,15 +28,13 @@
     virtual void InitSections() {
     }
 
-    virtual void SwitchSection(const MCSection *Section) {
-      PrevSection = CurSection;
-      CurSection = Section;
+    virtual void ChangeSection(const MCSection *Section) {
     }
 
     virtual void EmitLabel(MCSymbol *Symbol) {
       assert(Symbol->isUndefined() && "Cannot define a symbol twice!");
-      assert(CurSection && "Cannot emit before setting section!");
-      Symbol->setSection(*CurSection);
+      assert(getCurrentSection() && "Cannot emit before setting section!");
+      Symbol->setSection(*getCurrentSection());
     }
 
     virtual void EmitAssemblerFlag(MCAssemblerFlag Flag) {}