config: better (i.e. more portable) test for libxml2

Over the weekend I tried to build on MacOS X¹ and ran into the following
issues:
1) The recent change to autogen.sh to test for pkg-config falls down.
2) After removing the pkg-config test in autogen.sh, w/o pkg-config the
   PKG_CHECK_MODULES macro invocation in configure[.ac] falls down. N.B.
   Solaris users run into this too, even through there's a (broken)
   pkg-config package that can be installed.
3) There are other problems in the code related to fuse that are beyond the
   scope of this.

It seems that pkg-config is only a requirement for the definition of the
PKG_CHECK_MODULES macro used to detect libxml2. Since this seems to be
inherently unportable — at least to MacOS X and Solaris — I'd like to:
A) Change the use of the PKG_CHECK_MODULES macro to the more portable
   AM_PATH_XML2 macro provided by the libxml2 package in
   /usr/.../share/aclocal/libxml.m4
2) Revisit the decision to add the check for pkg-config in autogen.sh in
   BZ 921817.

For now this is just an rfc. If people are agreeable I'll reenter this
change against BZ 921817.

¹Mountain Lion 10.8.3, XCode 4.6.1

Change-Id: I237b1ed8919088345b8fd943423b2a6ad289981b
BUG: 921817
Signed-off-by: Kaleb S. KEITHLEY <kkeithle@redhat.com>
Reviewed-on: http://review.gluster.org/4720
Reviewed-by: Justin Clift <jclift@redhat.com>
Tested-by: Justin Clift <jclift@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>

autogen.sh

@@ -54,12 +54,6 @@ else
   fi
 fi
 
-# Check for pkg-config
-env pkg-config --version > /dev/null 2>&1
-if [ $? -ne 0 ]; then
-  MISSING="$MISSING pkg-config"
-fi
-
 # Check for tar
 env tar --version > /dev/null 2>&1
 if [ $? -ne 0 ]; then

cli/src/Makefile.am

@@ -10,7 +10,7 @@ endif
 gluster_LDADD = $(top_builddir)/libglusterfs/src/libglusterfs.la $(GF_LDADD)\
 		$(RLLIBS) $(top_builddir)/rpc/xdr/src/libgfxdr.la \
 		$(top_builddir)/rpc/rpc-lib/src/libgfrpc.la \
-		$(GF_GLUSTERFS_LIBS) $(LIBXML2_LIBS)
+		$(GF_GLUSTERFS_LIBS) $(XML_LIBS)
 
 gluster_LDFLAGS = $(GF_LDFLAGS)
 noinst_HEADERS = cli.h cli-mem-types.h cli-cmd.h
@@ -22,7 +22,7 @@ AM_CPPFLAGS = $(GF_CPPFLAGS) \
 	-DCONFDIR=\"$(sysconfdir)/glusterfs\" \
 	-DGSYNCD_PREFIX=\"$(libexecdir)/glusterfs\"\
 	-DSYNCDAEMON_COMPILE=$(SYNCDAEMON_COMPILE) -DSBIN_DIR=\"$(sbindir)\"\
-	$(LIBXML2_CFLAGS)
+	$(XML_CPPFLAGS)
 
 AM_CFLAGS = -Wall $(GF_GLUSTERFS_CFLAGS)
 

configure.ac

@@ -439,12 +439,11 @@ fi
 #check if libxml is present if so enable HAVE_LIB_XML
 echo -n "checking if libxml2 is present... "
 
-PKG_CHECK_MODULES([LIBXML2], [libxml-2.0 >= 2.6.19],
-                  [echo "yes (features requiring libxml2 enabled)"  AC_DEFINE([HAVE_LIB_XML], [1], [define if libxml2 is present])],
-                  [echo "no"] )
+AM_PATH_XML2([2.6.19])
 
-AC_SUBST(LIBXML2_CFLAGS)
-AC_SUBST(LIBXML2_LIBS)
+if test "x${no_xml}" = "x"; then
+    AC_DEFINE([HAVE_LIB_XML], [1], [Define to 1 if using libxml2.])
+fi
 
 dnl FreeBSD > 5 has execinfo as a Ported library for giving a workaround
 dnl solution to GCC backtrace functionality

xlators/mgmt/glusterd/src/Makefile.am

@@ -16,7 +16,7 @@ glusterd_la_SOURCES = glusterd.c glusterd-handler.c glusterd-sm.c \
 glusterd_la_LIBADD = $(top_builddir)/libglusterfs/src/libglusterfs.la \
 		     $(top_builddir)/rpc/xdr/src/libgfxdr.la \
 		     $(top_builddir)/rpc/rpc-lib/src/libgfrpc.la \
-		     $(LIBXML2_LIBS) -lcrypto
+		     $(XML_LIBS) -lcrypto
 
 noinst_HEADERS = glusterd.h glusterd-utils.h glusterd-op-sm.h \
 	glusterd-sm.h glusterd-store.h glusterd-mem-types.h \
@@ -29,7 +29,7 @@ AM_CPPFLAGS = $(GF_CPPFLAGS) -I$(top_srcdir)/libglusterfs/src \
 	-I$(CONTRIBDIR)/uuid \
 	-DSBIN_DIR=\"$(sbindir)\" -DDATADIR=\"$(localstatedir)\" \
 	-DGSYNCD_PREFIX=\"$(libexecdir)/glusterfs\"\
-        -DSYNCDAEMON_COMPILE=$(SYNCDAEMON_COMPILE) $(LIBXML2_CFLAGS)
+        -DSYNCDAEMON_COMPILE=$(SYNCDAEMON_COMPILE) $(XML_CPPFLAGS)
 
 AM_CFLAGS = -Wall $(GF_CFLAGS)