[libxml2] Disable xmlExp regex code

[Nick Wellnhofer <nwellnhof src gnome org>]

commit d56184a0859aaf6873a3886b43a9638e9cf9f167
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Thu Sep 26 12:11:39 2019 +0200

    Disable xmlExp regex code
    
    This is apparently another regex engine that was never used, see commit
    81a8ec6.

 Makefile.am                    | 3 +++
 include/libxml/xmlversion.h.in | 4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)
---
diff --git a/Makefile.am b/Makefile.am
index d43149fb..05d1671f 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -915,6 +915,9 @@ Regexptests: testRegexp$(EXEEXT)
              if [ -n "$$log" ] ; then echo $$name result ; echo "$$log" ; fi ; \
              rm result.$$name ; \
          fi ; fi ; done)
+
+# Disabled for now
+Exptests: testRegexp$(EXEEXT)
        @echo "## Formal expresssions regression tests"
        -@(for i in $(srcdir)/test/expr/* ; do \
          name=`basename $$i`; \
diff --git a/include/libxml/xmlversion.h.in b/include/libxml/xmlversion.h.in
index 5ba64f23..964f10d8 100644
--- a/include/libxml/xmlversion.h.in
+++ b/include/libxml/xmlversion.h.in
@@ -350,8 +350,10 @@ XMLPUBFUN void XMLCALL xmlCheckVersion(int version);
  * LIBXML_EXPR_ENABLED:
  *
  * Whether the formal expressions interfaces are compiled in
+ *
+ * This code is unused and disabled unconditionally for now.
  */
-#if @WITH_SCHEMAS@
+#if 0
 #define LIBXML_EXPR_ENABLED
 #endif