Prevent NULL from ever pointing to some real code or data. (This was

causing the serial console to ignore input, because it happened to end up
linked with serial_ischar() at address 0, which core/console.c decided was
invalid).

src/arch/i386/scripts/i386-kir.lds

     . = _text16_link_addr;
     _text16 = .;
 
+    . += 1;			/* Prevent NULL being valid */
+
     .text16 : AT ( _text16_load_offset + __text16 ) {
 	__text16 = .;
 	*(.text.null_trap)
     . = _data16_link_addr;
     _data16 = .;
 
+    . += 1;			/* Prevent NULL being valid */
+
     .rodata16 : AT ( _data16_load_offset + __rodata16 ) {
 	__rodata16 = .;
 	*(.rodata16)

src/arch/i386/scripts/i386.lds

     . = _text16_link_addr;
     _text16 = .;
 
+    . += 1;			/* Prevent NULL being valid */
+
     .text16 : AT ( _text16_load_offset + __text16 ) {
 	__text16 = .;
 	*(.text16)
     . = _data16_link_addr;
     _data16 = .;
 
+    . += 1;			/* Prevent NULL being valid */
+
     .rodata16 : AT ( _data16_load_offset + __rodata16 ) {
 	__rodata16 = .;
 	*(.rodata16)
 
     _text = .;
 
+    . += 1;			/* Prevent NULL being valid */
+
     .text : AT ( _textdata_load_offset + __text ) {
 	__text = .;
 	*(.text.null_trap)