Fix crash when when do lto on Bullet. Dynamic GEPs in SROA were incorrectly...

Fix crash when when do lto on Bullet.  Dynamic GEPs in SROA were incorrectly being applied to all accesses to an alloca, not just the ones which read from the GEP.  Thanks to Evan for reducing the test.  rdar://11861001

llvm-svn: 161654