Use ACX_NONCANONICAL_TARGET in gdb/configure

Shahab Vahedi pointed out that the patch to remove
gdb/testsuite/configure regressed the site.exp creation a bit -- it
left an unresolved configure substitution.  Andrew Burgess pointed out
that the patch removed the call to ACX_NONCANONICAL_TARGET, which
caused this problem.

This patch adds ACX_NONCANONICAL_TARGET to gdb's configure, and fixes
the bug.

gdb/ChangeLog
2021-06-05  Tom Tromey  <tromey@adacore.com>

	* configure: Rebuild.
	* configure.ac: Add ACX_NONCANONICAL_TARGET.

gdb/configure

@@ -800,6 +800,7 @@ DEPDIR
 am__leading_dot
 CXX_DIALECT
 HAVE_CXX11
+target_noncanonical
 INSTALL_STRIP_PROGRAM
 STRIP
 install_sh
@@ -5186,6 +5187,24 @@ ac_configure="$SHELL $ac_aux_dir/configure"  # Please don't use this var.
 # Set target, target_cpu, target_vendor, and target_os.
 
 
+ case ${build_alias} in
+  "") build_noncanonical=${build} ;;
+  *) build_noncanonical=${build_alias} ;;
+esac
+
+ case ${host_alias} in
+  "") host_noncanonical=${build_noncanonical} ;;
+  *) host_noncanonical=${host_alias} ;;
+esac
+
+ case ${target_alias} in
+  "") target_noncanonical=${host_noncanonical} ;;
+  *) target_noncanonical=${target_alias} ;;
+esac
+
+
+
+
 test "$program_prefix" != NONE &&
   program_transform_name="s&^&$program_prefix&;$program_transform_name"
 # Use a double $ so make ignores it.