Store a bit in MCSection saying if it was registered with MCAssembler.

With this we can replace a SetVector with a plain std::vector.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@238706 91177308-0d34-0410-b5e6-96231b3b80d8

lib/MC/MCSection.cpp

@@ -21,7 +21,7 @@ using namespace llvm;
 
 MCSection::MCSection(SectionVariant V, SectionKind K, MCSymbol *Begin)
     : Begin(Begin), BundleGroupBeforeFirstInst(false), HasInstructions(false),
-      Variant(V), Kind(K) {}
+      IsRegistered(false), Variant(V), Kind(K) {}
 
 MCSymbol *MCSection::getEndSymbol(MCContext &Ctx) {
   if (!End)