gdb, gdbserver, gdbsupport: use AC_CANONICAL_{BUILD,HOST,TARGET} instead of AC_CANONICAL_SYSTEM

`autoreconf -Wall` notes that AC_CANONICAL_SYSTEM is obsolete:

    configure.ac:36: warning: The macro `AC_CANONICAL_SYSTEM' is obsolete.

Replace it by AC_CANONICAL_BUILD, AC_CANONICAL_HOST and
AC_CANONICAL_TARGET in configure.ac files in gdb, gdbserver and
gdbsupport.  All three macros may not be needed everywhere, but it is
hard to completely audit the configure files to see which are required,
so I think it's better (and that there's no downside) to just call all
three.

gdb/ChangeLog:

	* configure.ac: Use AC_CANONICAL_{BUILD,HOST,TARGET} instead of
	AC_CANONICAL_SYSTEM.
	* configure: Re-generate.

gdbserver/ChangeLog:

	* configure.ac: Use AC_CANONICAL_{BUILD,HOST,TARGET} instead of
	AC_CANONICAL_SYSTEM.
	* configure: Re-generate.

gdbsupport/ChangeLog:

	* configure.ac: Use AC_CANONICAL_{BUILD,HOST,TARGET} instead of
	AC_CANONICAL_SYSTEM.
	* configure: Re-generate.

Change-Id: Ifd0e21f1e478634e768b5de1b8ee06a7f690d863

gdbserver/configure

@@ -4588,6 +4588,7 @@ fi
 INSTALL_STRIP_PROGRAM="\$(install_sh) -c -s"
 
 
+# Set build, build_cpu, build_vendor and build_os.
 # Make sure we can run config.sub.
 $SHELL "$ac_aux_dir/config.sub" sun4 >/dev/null 2>&1 ||
   as_fn_error $? "cannot run $SHELL $ac_aux_dir/config.sub" "$LINENO" 5
@@ -4626,6 +4627,8 @@ IFS=$ac_save_IFS
 case $build_os in *\ *) build_os=`echo "$build_os" | sed 's/ /-/g'`;; esac
 
 
+
+# Set host, host_cpu, host_vendor, and host_os.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking host system type" >&5
 $as_echo_n "checking host system type... " >&6; }
 if ${ac_cv_host+:} false; then :
@@ -4659,6 +4662,8 @@ IFS=$ac_save_IFS
 case $host_os in *\ *) host_os=`echo "$host_os" | sed 's/ /-/g'`;; esac
 
 
+
+# Set target, target_cpu, target_vendor, and target_os.
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking target system type" >&5
 $as_echo_n "checking target system type... " >&6; }
 if ${ac_cv_target+:} false; then :
@@ -4699,7 +4704,6 @@ test -n "$target_alias" &&
     NONENONEs,x,x, &&
   program_prefix=${target_alias}-
 
-
 # Find a good install program.  We prefer a C program (faster),
 # so one script is as good as another.  But avoid the broken or
 # incompatible versions: