[libxslt] Check whether 'xml2-config --dynamic' is supported

[Nick Wellnhofer <nwellnhof src gnome org>]

commit bde9dc85b3a91894c91bbc9ae84b13e49c363f4d
Author: Nick Wellnhofer <wellnhofer aevum de>
Date:   Mon Nov 11 12:05:31 2019 +0100

    Check whether 'xml2-config --dynamic' is supported
    
    Fixes build with older libxml2 versions.
    
    Closes #22.

 configure.ac | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)
---
diff --git a/configure.ac b/configure.ac
index 325a7bea..3da57b18 100644
--- a/configure.ac
+++ b/configure.ac
@@ -491,6 +491,7 @@ dnl
 
 build_shared_libs="yes"
 build_static_libs="yes"
+xml_config_dynamic=
 
 if test "$enable_shared" = "no"; then
     build_shared_libs="no"
@@ -515,10 +516,11 @@ if test "x$LIBXML_SRC" != "x"; then
         XML_CONFIG="${LIBXML_SRC}/xml2-config"
         LIBXML_CFLAGS="-I${LIBXML_SRC}/include"
         if test "$build_static_libs" = "no"; then
-            LIBXML_LIBS="-L${LIBXML_SRC} `$XML_CONFIG --libs --dynamic`"
-        else
-            LIBXML_LIBS="-L${LIBXML_SRC} `$XML_CONFIG --libs`"
+            if $XML_CONFIG --help | grep -q '\--dynamic'; then
+                xml_config_dynamic=--dynamic
+            fi
         fi
+        LIBXML_LIBS="-L${LIBXML_SRC} `$XML_CONFIG --libs $xml_config_dynamic`"
         WITH_MODULES="`$XML_CONFIG --modules`"
         cd $CWD
     else
@@ -557,12 +559,13 @@ then
     fi
 
     if test "$build_static_libs" = "no"; then
-        LIBXML_LIBS="`$XML_CONFIG --libs --dynamic`"
-    else
-        LIBXML_LIBS="`$XML_CONFIG --libs`"
+        if $XML_CONFIG --help | grep -q '\--dynamic'; then
+            xml_config_dynamic=--dynamic
+        fi
     fi
-       LIBXML_CFLAGS="`$XML_CONFIG --cflags`"
-        WITH_MODULES="`$XML_CONFIG --modules`"
+    LIBXML_LIBS="`$XML_CONFIG --libs $xml_config_dynamic`"
+    LIBXML_CFLAGS="`$XML_CONFIG --cflags`"
+    WITH_MODULES="`$XML_CONFIG --modules`"
 fi
 
 if test "x$LIBXML_LIBS" = "x"