Avoid to record execontext used for origin tracking when --trac-origins=no
All calls to VG_(unknown_SP_update) were recording an execontext
of one IP, useful only for track origin.
This patch implements splits VG_(unknown_SP_update) 
in two different functions VG_(unknown_SP_update_w_ECU)
(doing origin tracking) and VG_(unknown_SP_update)  (not doing origin tracking).




git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13225 a5019735-40e9-0310-863c-91ae7b9d1cf9