[libxml2] Disable docbook support by default

[Nick Wellnhofer <nwellnhof src gnome org>]

commit aeaf02c0a3e8cf2df8dfcfe7d73b1378beffc0f0
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Sun Feb 20 20:51:20 2022 +0100

    Disable docbook support by default
    
    The docbook code is broken and has been deprecated for years.

 configure.ac | 10 +++-------
 1 file changed, 3 insertions(+), 7 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 6d4ba8e3..dea488e1 100644
--- a/configure.ac
+++ b/configure.ac
@@ -98,7 +98,7 @@ AC_ARG_WITH(catalog,
 AC_ARG_WITH(debug,
 [  --with-debug            add the debugging module (on)])
 AC_ARG_WITH(docbook,
-[  --with-docbook          add Docbook SGML support (on)])
+[  --with-docbook          add Docbook SGML support (off)])
 AC_ARG_WITH(fexceptions,
 [  --with-fexceptions      add GCC flag -fexceptions for C++ exceptions (off)])
 AC_ARG_WITH(ftp,
@@ -246,10 +246,6 @@ then
     then
       with_debug=no
     fi
-    if test "$with_docbook" = ""
-    then
-      with_docbook=no
-    fi
     if test "$with_fexceptions" = ""
     then
       with_fexceptions=no
@@ -968,7 +964,7 @@ if [[ "${LOGNAME}" = "veillard" -a "`pwd`" = "/u/veillard/XML" ]] || \
            with_run_debug="yes"
        fi
        if test "${with_docbook}" = "" ; then
-           with_docbook="yes"
+           with_docbook="no"
        fi
     fi
     if test "${GCC}" = "yes" ; then
@@ -1266,7 +1262,7 @@ AC_SUBST(WITH_CATALOG)
 AC_SUBST(CATALOG_OBJ)
 AC_SUBST(TEST_CATALOG)
 
-if test "$with_docbook" = "no" ; then
+if test "$with_docbook" != "yes" ; then
     echo Disabling Docbook support
     WITH_DOCB=0
     DOCB_OBJ=