Increase the size of DwarfAccelTable::TableHeaderData::Atoms.

During a Clang bootstrap, it seems this SmallVector always contains 3 elements.

llvm-svn: 215334
diff --git a/llvm/lib/CodeGen/AsmPrinter/DwarfAccelTable.h b/llvm/lib/CodeGen/AsmPrinter/DwarfAccelTable.h
index a3cc95f..3bfb0a6 100644
--- a/llvm/lib/CodeGen/AsmPrinter/DwarfAccelTable.h
+++ b/llvm/lib/CodeGen/AsmPrinter/DwarfAccelTable.h
@@ -140,7 +140,7 @@
 private:
   struct TableHeaderData {
     uint32_t die_offset_base;
-    SmallVector<Atom, 1> Atoms;
+    SmallVector<Atom, 3> Atoms;
 
     TableHeaderData(ArrayRef<Atom> AtomList, uint32_t offset = 0)
         : die_offset_base(offset), Atoms(AtomList.begin(), AtomList.end()) {}