Don't include WIN64/EFI64 for x32

Since x32 doesn't support WIN64/EFI64, don't include it for x32.  Also
x32 has sizeof size_t == 4.  But TARGET should be X86_64.

configure.host

@@ -106,10 +106,18 @@ case "${host}" in
 	if test $ac_cv_sizeof_size_t = 4; then
 	  case "$host" in
 	    x86_64-*x32|x86_64-x32-*)
+	      TARGET_X32=yes
 	      TARGET=X86_64
 	      ;;
 	    *)
-	      TARGET=X86
+	      echo 'int foo (void) { return __x86_64__; }' > conftest.c
+	      if $CC $CFLAGS -Werror -S conftest.c -o conftest.s > /dev/null 2>&1; then
+		TARGET_X32=yes
+		TARGET=X86_64
+	      else
+		TARGET=X86;
+	      fi
+	      rm -f conftest.*
 	      ;;
           esac
 	else
@@ -255,7 +263,11 @@ case "${TARGET}" in
 	SOURCES="ffi.c sysv.S"
 	;;
   X86_64)
-	SOURCES="ffi64.c unix64.S ffiw64.c win64.S"
+	if test x"$TARGET_X32" = xyes; then
+		SOURCES="ffi64.c unix64.S"
+	else
+		SOURCES="ffi64.c unix64.S ffiw64.c win64.S"
+	fi
 	;;
   X86_WIN64)
 	if test "$MSVC" = 1; then