Update ax_boost_system.m4 to serial 17

- Use 'ls -r' rather than non-portable tool 'tac'. Simplify filepattern in ls expression so dylib (on OSX) are also detected.

src/m4/ax_boost_system.m4

@@ -31,7 +31,7 @@
 #   and this notice are preserved. This file is offered as-is, without any
 #   warranty.
 
-#serial 14
+#serial 17
 
 AC_DEFUN([AX_BOOST_SYSTEM],
 [
@@ -83,14 +83,14 @@ 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*.so* $BOOSTLIBDIR/libboost_system*.a* 2>/dev/null | sed 's,.*/,,' | sed -e 's;^lib\(boost_system.*\)\.so.*$;\1;' -e 's;^lib\(boost_system.*\)\.a*$;\1;'` ; 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.*$;\1;' -e 's;^\(boost_system.*\)\.a*$;\1;'` ; 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],