This fixes the shadow validity setup of SP,IA and FPC. The current
code misses a char * cast and thus uses a wrong pointer for memset.
This resulted in corruptions of a thread state for multi threaded
programs. After vex: r2818 the memset did overwrite the tid value
of a thread, making this bug visible.
Lets use the c structures instead of pointer arithmetics.



git-svn-id: svn://svn.valgrind.org/valgrind/trunk@13838 a5019735-40e9-0310-863c-91ae7b9d1cf9