[OutputSection] Set the symbolic bit in DT_FLAGS and not DT_FLAGS_1.

The two names are similar enough that they might lead to confusion.
The output of readobj clarifies but I missed it when I originally
committed this. Found while linking FreeBSD userland with lld.

llvm-svn: 250739
diff --git a/lld/ELF/OutputSections.cpp b/lld/ELF/OutputSections.cpp
index 1775562..8066070 100644
--- a/lld/ELF/OutputSections.cpp
+++ b/lld/ELF/OutputSections.cpp
@@ -369,6 +369,9 @@
   uint32_t Flags = 0;
   if (Config->Bsymbolic)
     Flags |= DF_SYMBOLIC;
+  if (Flags)
+    WriteVal(DT_FLAGS, Flags);
+  Flags = 0;
   if (Config->ZNow)
     Flags |= DF_1_NOW;
   if (Flags)