Pull newer m4/ax_boost_system.m4 from upstream.

Does not require tac, which is not available on *BSD/OS X.

Change-Id: I54c90e249fb99ce03cc2ff134f200de283159052
Reviewed-on: https://gerrit.libreoffice.org/22083Reviewed-by: Michael Stahl <mstahl@redhat.com>
Tested-by: Michael Stahl <mstahl@redhat.com>

m4/ax_boost_system.m4

@@ -31,7 +31,7 @@
 #   and this notice are preserved. This file is offered as-is, without any
 #   warranty.
 
-#serial 15
+#serial 18
 
 AC_DEFUN([AX_BOOST_SYSTEM],
 [
@@ -68,9 +68,10 @@ AC_DEFUN([AX_BOOST_SYSTEM],
 					   ax_cv_boost_system,
         [AC_LANG_PUSH([C++])
 			 CXXFLAGS_SAVE=$CXXFLAGS
+			 CXXFLAGS=
 
 			 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[@%:@include <boost/system/error_code.hpp>]],
-                                   [[boost::system::system_category]])],
+				    [[boost::system::error_category *a = 0;]])],
                    ax_cv_boost_system=yes, ax_cv_boost_system=no)
 			 CXXFLAGS=$CXXFLAGS_SAVE
              AC_LANG_POP([C++])
@@ -83,14 +84,14 @@ AC_DEFUN([AX_BOOST_SYSTEM],
 
 			LDFLAGS_SAVE=$LDFLAGS
             if test "x$ax_boost_user_system_lib" = "x"; then
-                for libextension in `ls $BOOSTLIBDIR/libboost_system*.a* $BOOSTLIBDIR/libboost_system*.so* 2>/dev/null | sed 's,.*/,,' | sed -e 's;^lib\(boost_system.*\)\.\(so\|a\).*$;\1;' | tac` ; do
+                for libextension in `ls -r $BOOSTLIBDIR/libboost_system* 2>/dev/null | sed 's,.*/lib,,' | sed 's,\..*,,'` ; do
                      ax_lib=${libextension}
 				    AC_CHECK_LIB($ax_lib, exit,
                                  [BOOST_SYSTEM_LIB="-l$ax_lib"; AC_SUBST(BOOST_SYSTEM_LIB) link_system="yes"; break],
                                  [link_system="no"])
 				done
                 if test "x$link_system" != "xyes"; then
-                for libextension in `ls $BOOSTLIBDIR/boost_system*.{dll,a}* 2>/dev/null | sed 's,.*/,,' | sed -e 's;^\(boost_system.*\)\.\(dll\|a\).*$;\1;' | tac` ; do
+                for libextension in `ls -r $BOOSTLIBDIR/boost_system* 2>/dev/null | sed 's,.*/,,' | sed -e 's,\..*,,'` ; do
                      ax_lib=${libextension}
 				    AC_CHECK_LIB($ax_lib, exit,
                                  [BOOST_SYSTEM_LIB="-l$ax_lib"; AC_SUBST(BOOST_SYSTEM_LIB) link_system="yes"; break],