Teach llvm-readobj to print human friendly description of reserved sections.

llvm-svn: 204584
diff --git a/llvm/test/MC/ELF/pic-diff.s b/llvm/test/MC/ELF/pic-diff.s
index cffa0dd..30c9278 100644
--- a/llvm/test/MC/ELF/pic-diff.s
+++ b/llvm/test/MC/ELF/pic-diff.s
@@ -13,7 +13,7 @@
 // CHECK-NEXT:     Binding: Global
 // CHECK-NEXT:     Type: None
 // CHECK-NEXT:     Other: 0
-// CHECK-NEXT:     Section: (0x0)
+// CHECK-NEXT:     Section: Undefined (0x0)
 // CHECK-NEXT:   }
 
 .zero 4