doc: add xreflabel for libpq chapter, needed for PG 14 relnotes

bmomjian · bmomjian · commit 1e7d53bd019e · 2021-05-19T11:01:28.000-04:00
diff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgml
@@ -1,6 +1,6 @@
 <!-- doc/src/sgml/libpq.sgml -->
 
-<chapter id="libpq">
+<chapter id="libpq" xreflabel="libpq">
  <title><application>libpq</application> &mdash; C Library</title>
 
  <indexterm zone="libpq">
