Cygwin 1.7 has thread-safe pread

Per http://cygwin.com/ml/cygwin/2012-07/msg00331.html , cygwin 1.7
was modified to explicitly support git's use of pread, so make this
the default. Do not affect earlier cygwin versions.

Signed-off-by: Mark Levedahl <mlevedahl@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

config.mak.uname

@@ -159,10 +159,10 @@ ifeq ($(uname_O),Cygwin)
 		NO_SYMLINK_HEAD = YesPlease
 		NO_IPV6 = YesPlease
 		OLD_ICONV = UnfortunatelyYes
+		NO_THREAD_SAFE_PREAD = YesPlease
 	else
 		NO_REGEX = UnfortunatelyYes
 	endif
-	NO_THREAD_SAFE_PREAD = YesPlease
 	NEEDS_LIBICONV = YesPlease
 	NO_FAST_WORKING_DIRECTORY = UnfortunatelyYes
 	NO_TRUSTABLE_FILEMODE = UnfortunatelyYes