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/MCStreamer.cpp b/lib/MC/MCStreamer.cpp
index 1cb5165..3dcdba1 100644
--- a/lib/MC/MCStreamer.cpp
+++ b/lib/MC/MCStreamer.cpp
@@ -19,8 +19,9 @@
 #include <cstdlib>
 using namespace llvm;
 
-MCStreamer::MCStreamer(MCContext &Ctx) : Context(Ctx), CurSection(0),
-                                         PrevSection(0) {
+MCStreamer::MCStreamer(MCContext &Ctx) : Context(Ctx) {
+  PrevSectionStack.push_back(NULL);
+  CurSectionStack.push_back(NULL);
 }
 
 MCStreamer::~MCStreamer() {