Many small changes to procfs.c to add base support for a new "info proc"

command that prints /proc specific information, changes to solib.c to
allow more flexible handling of finding the dynamic linker structures,
changes to utils.c and defs.h to add a new null_cleanup() function to
serve as an anchor point for cleanup chains with no obvious "first
cleanup".

gdb/xm-sysv4.h

@@ -18,6 +18,10 @@ You should have received a copy of the GNU General Public License
 along with this program; if not, write to the Free Software
 Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
 
+/* Use SVR4 style shared library support */
+
+#define SVR4_SHARED_LIBS
+
 /* SVR4 has /proc support, so use it instead of ptrace. */
 
 #define USE_PROC_FS