Port Unicode char detection to FreeBSD+svgalib

Problem reported by Ashish SHUKLA in:
http://lists.gnu.org/archive/html/emacs-devel/2015-09/msg00531.html
* configure.ac: Check for struct unipair.unicode instead of for
<linux/kd.h>, since that’s more specific to what the code actually needs.
* src/terminal.c: Use HAVE_STRUCT_UNIPAIR_UNICODE, not HAVE_LINUX_KD_H.

configure.ac

@@ -1582,7 +1582,6 @@ fi
 
 dnl checks for header files
 AC_CHECK_HEADERS_ONCE(
-  linux/kd.h
   sys/systeminfo.h
   sys/sysinfo.h
   coff.h pty.h
@@ -3999,6 +3998,8 @@ AC_SUBST(KRB4LIB)
 
 AC_CHECK_HEADERS(valgrind/valgrind.h)
 
+AC_CHECK_MEMBERS([struct unipair.unicode], [], [], [[#include <linux/kd.h>]])
+
 AC_CHECK_FUNCS_ONCE(tzset)
 
 ok_so_far=yes

src/terminal.c

@@ -28,7 +28,7 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include "coding.h"
 #include "keyboard.h"
 
-#ifdef HAVE_LINUX_KD_H
+#if HAVE_STRUCT_UNIPAIR_UNICODE
 # include <errno.h>
 # include <linux/kd.h>
 # include <sys/ioctl.h>
@@ -532,7 +532,7 @@ selected frame's terminal).  */)
   return store_terminal_param (decode_live_terminal (terminal), parameter, value);
 }
 
-#if HAVE_LINUX_KD_H
+#if HAVE_STRUCT_UNIPAIR_UNICODE
 
 /* Compute the glyph code table for T.  */
 
@@ -575,7 +575,7 @@ calculate_glyph_code_table (struct terminal *t)
 Lisp_Object
 terminal_glyph_code (struct terminal *t, int ch)
 {
-#if HAVE_LINUX_KD_H
+#if HAVE_STRUCT_UNIPAIR_UNICODE
   if (t->type == output_termcap)
     {
       /* As a hack, recompute the table when CH is the maximum