python3: Enable FreeBSD cross build

This only enables x86_64-unknown-freebsd, not any other FreeBSD, since I
do not have any other machines to tests on. If you're reading this, feel
free to try out other arches!

Signed-off-by: Jörg Thalheim <joerg@thalheim.io>

Author: rhelmot

configure.ac

@@ -339,6 +339,9 @@ then
 	*-*-wasi)
 	    ac_sys_system=WASI
 	    ;;
+	*-*-freebsd)
+	    ac_sys_system=FreeBSD
+	    ;;
 	*)
 		# for now, limit cross builds to known configurations
 		MACHDEP="unknown"
@@ -452,6 +455,9 @@ AC_ARG_ENABLE([universalsdk],
 		UNIVERSALSDK=
 		enable_universalsdk=
 		;;
+	x86_64-*-freebsd)
+		_host_cpu=x86_64
+		;;
 	*)
 		UNIVERSALSDK=$enableval
 		if test ! -d "${UNIVERSALSDK}"