Close unique sections when switching away from them.

It is not possible to switch back to unique secitons, so close them
automatically when switching away.

llvm-svn: 233380
diff --git a/llvm/lib/MC/MCSectionMachO.cpp b/llvm/lib/MC/MCSectionMachO.cpp
index c9f1591..606d074 100644
--- a/llvm/lib/MC/MCSectionMachO.cpp
+++ b/llvm/lib/MC/MCSectionMachO.cpp
@@ -72,7 +72,7 @@
 MCSectionMachO::MCSectionMachO(StringRef Segment, StringRef Section,
                                unsigned TAA, unsigned reserved2, SectionKind K,
                                MCSymbol *Begin)
-    : MCSection(SV_MachO, K, Begin), TypeAndAttributes(TAA),
+    : MCSection(SV_MachO, K, Begin, /*Unique*/ false), TypeAndAttributes(TAA),
       Reserved2(reserved2) {
   assert(Segment.size() <= 16 && Section.size() <= 16 &&
          "Segment or section string too long");