libphobos: Add power*-*-freebsd* as supported target

This has been tested on powerpc64-freebsd13 and powerpc64le-freebsd13,
and used to build dub, along with some D tools from ports.

libphobos/ChangeLog:

	* configure.tgt: Add power*-*-freebsd* as a supported target.

libphobos/configure.tgt

@@ -39,6 +39,9 @@ case "${target}" in
   mips*-*-linux*)
 	LIBPHOBOS_SUPPORTED=yes
 	;;
+  power*-*-freebsd*)
+	LIBPHOBOS_SUPPORTED=yes
+	;;
   power*-*-linux*)
 	LIBPHOBOS_SUPPORTED=yes
 	LIBDRUNTIME_ONLY=yes