Makefile: enable THREADED_DELTA_SEARCH on SunOS

Signed-off-by: NBrandon Casey <casey@nrlssc.navy.mil>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Makefile

@@ -734,6 +734,7 @@ ifeq ($(uname_S),SunOS)
 	NO_MKSTEMPS = YesPlease
 	NO_REGEX = YesPlease
 	NO_EXTERNAL_GREP = YesPlease
+	THREADED_DELTA_SEARCH = YesPlease
 	ifeq ($(uname_R),5.7)
 		NEEDS_RESOLV = YesPlease
 		NO_IPV6 = YesPlease