Handle ICU_LIBS as LIBADD, not LDFLAGS to prevent linking errors

For https://bugzilla.gnome.org/show_bug.cgi?id=677606
For https://bugs.gentoo.org/show_bug.cgi?id=417539

If libxml2-2.8.0 is built with --with-icu --with-python on a system that has an
older version of libxml2 installed, then during "make install", libxml2mod.so
gets relinked to the systemwide version of libxml2.so.2 instead of libxml2.so.2
from the build tree, and fails at runtime if symbol versions from the older
libxml2.so.2 are not available. This effectively makes it impossible to build a
libxml2-2.8.0 binary package on a system that does not already have
libxml2-2.8.0 installed.

Investigation by Rafał Mużyło and Arfrever Frehtes Taifersar Arahesis revealed
the cause of the problem to be that libxml2's configure was adding ICU_LIBS to
LDFLAGS instead of to LIBADD. This resulted in GNU libtool using the wrong
argument order in its relinking command that gets run during "make install".

Makefile.am

@@ -20,7 +20,7 @@ bin_PROGRAMS = xmllint xmlcatalog
 bin_SCRIPTS=xml2-config
 
 lib_LTLIBRARIES = libxml2.la
-libxml2_la_LIBADD = $(THREAD_LIBS) $(Z_LIBS) $(LZMA_LIBS) $(ICONV_LIBS) $(M_LIBS) $(WIN32_EXTRA_LIBADD)
+libxml2_la_LIBADD = $(ICU_LIBS) $(THREAD_LIBS) $(Z_LIBS) $(LZMA_LIBS) $(ICONV_LIBS) $(M_LIBS) $(WIN32_EXTRA_LIBADD)
 
 if USE_VERSION_SCRIPT
 LIBXML2_VERSION_SCRIPT = $(VERSION_SCRIPT_FLAGS)$(srcdir)/libxml2.syms

configure.in

@@ -98,7 +98,7 @@ dnl
 dnl zlib option might change flags, so we save them initially
 dnl
 _cppflags="${CPPFLAGS}"
-_ldflags="${LDFLAGS}"
+_libs="${LIBS}"
 
 AC_ARG_WITH(c14n,
 [  --with-c14n             add the Canonicalization support (on)])
@@ -155,7 +155,7 @@ AC_ARG_WITH(readline,
   if test "$withval" != "no" -a "$withval" != "yes"; then
     RDL_DIR=$withval
     CPPFLAGS="${CPPFLAGS} -I$withval/include"
-    LDFLAGS="${LDFLAGS} -L$withval/lib"
+    LIBS="${LIBS} -L$withval/lib"
   fi
 ])
 AC_ARG_WITH(regexps,
@@ -191,7 +191,7 @@ AC_ARG_WITH(zlib,
   if test "$withval" != "no" -a "$withval" != "yes"; then
     Z_DIR=$withval
     CPPFLAGS="${CPPFLAGS} -I$withval/include"
-    LDFLAGS="${LDFLAGS} -L$withval/lib"
+    LIBS="${LIBS} -L$withval/lib"
   fi
 ])
 AC_ARG_WITH(lzma,
@@ -199,7 +199,7 @@ AC_ARG_WITH(lzma,
   if test "$withval" != "no" -a "$withval" != "yes"; then
     LZMA_DIR=$withval
     CPPFLAGS="${CPPFLAGS} -I$withval/include"
-    LDFLAGS="${LDFLAGS} -L$withval/lib"
+    LIBS="${LIBS} -L$withval/lib"
   fi
 ])
 AC_ARG_WITH(coverage,
@@ -429,7 +429,7 @@ AC_SUBST(LZMA_LIBS)
 AC_SUBST(WITH_LZMA)
 
 CPPFLAGS=${_cppflags}
-LDFLAGS=${_ldflags}
+LIBS=${_libs}
 
 echo Checking headers
 
@@ -1378,14 +1378,14 @@ XML_LIBTOOLLIBS="libxml2.la"
 AC_SUBST(WITH_ICONV)
 
 WITH_ICU=0
+ICU_LIBS=""
 if test "$with_icu" != "yes" ; then
     echo Disabling ICU support
 else
     ICU_CONFIG=icu-config
     if ${ICU_CONFIG} --cflags >/dev/null 2>&1
     then
-        ICU_LIBS=`icu-config --ldflags`
-        LDFLAGS="$LDFLAGS $ICU_LIBS"
+        ICU_LIBS=`${ICU_CONFIG} --ldflags`
         WITH_ICU=1
         echo Enabling ICU support
     else
@@ -1393,6 +1393,7 @@ else
     fi
 fi
 AC_SUBST(WITH_ICU)
+AC_SUBST(ICU_LIBS)
 
 WITH_ISO8859X=1
 if test "$WITH_ICONV" != "1" ; then

libxml-2.0-uninstalled.pc.in

@@ -8,5 +8,5 @@ Name: libXML
 Version: @VERSION@
 Description: libXML library version2.
 Requires:
-Libs: -L${libdir} -lxml2 @THREAD_LIBS@ @Z_LIBS@ @ICONV_LIBS@ @M_LIBS@ @LIBS@
+Libs: -L${libdir} -lxml2 @ICU_LIBS@ @THREAD_LIBS@ @Z_LIBS@ @ICONV_LIBS@ @M_LIBS@ @LIBS@
 Cflags: -I${includedir} @XML_INCLUDEDIR@ @XML_CFLAGS@

libxml-2.0.pc.in

@@ -9,5 +9,5 @@ Version: @VERSION@
 Description: libXML library version2.
 Requires:
 Libs: -L${libdir} -lxml2
-Libs.private: @THREAD_LIBS@ @Z_LIBS@ @ICONV_LIBS@ @M_LIBS@ @WIN32_EXTRA_LIBADD@ @LIBS@
+Libs.private: @ICU_LIBS@ @THREAD_LIBS@ @Z_LIBS@ @ICONV_LIBS@ @M_LIBS@ @WIN32_EXTRA_LIBADD@ @LIBS@
 Cflags: @XML_INCLUDEDIR@ @XML_CFLAGS@