ax_boost_system.m4 uses "tac" which is not portable, OS X has "tail -r"

(Still, did not manage yet to build liborcus against boost 1.53 on OS X.)

Change-Id: I29b3e032badfe2e3631cd5f79f8c9e7bb0627dc8

liborcus/UnpackedTarball_orcus.mk

@@ -21,6 +21,11 @@ orcus_patches += liborcus_0.1.0-configure.patch
 # don't use dllimport
 orcus_patches += liborcus_0.1.0-dllimport.patch
 
+ifeq ($(OS),MACOSX)
+# no "tac" command on OS X, but "tail -r"
+orcus_patches += liborcus_0.1.0-tac.patch
+endif
+
 # <https://gitorious.org/orcus/orcus/merge_requests/2#
 # f60d6eecee72349993a392a9a63ddf3383d3b8c8-
 # f60d6eecee72349993a392a9a63ddf3383d3b8c8@2>:

liborcus/liborcus_0.1.0-tac.patch

+--- configure
++++ configure
+@@ -15668,7 +15668,7 @@
+ 
+ 			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 $BOOSTLIBDIR/libboost_system*.a* $BOOSTLIBDIR/libboost_system*.so* 2>/dev/null | sed 's,.*/,,' | sed -e 's;^lib\(boost_system.*\)\.\(so\|a\).*$;\1;' | tail -r` ; do
+                      ax_lib=${libextension}
+ 				    as_ac_Lib=`$as_echo "ac_cv_lib_$ax_lib''_exit" | $as_tr_sh`
+ { $as_echo "$as_me:${as_lineno-$LINENO}: checking for exit in -l$ax_lib" >&5
+@@ -15716,7 +15716,7 @@
+ 
+ 				done
+                 if test "x$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 $BOOSTLIBDIR/boost_system*.{dll,a}* 2>/dev/null | sed 's,.*/,,' | sed -e 's;^\(boost_system.*\)\.\(dll\|a\).*$;\1;' | tail -r` ; do
+                      ax_lib=${libextension}
+ 				    as_ac_Lib=`$as_echo "ac_cv_lib_$ax_lib''_exit" | $as_tr_sh`
+ { $as_echo "$as_me:${as_lineno-$LINENO}: checking for exit in -l$ax_lib" >&5