[CodeGen] stop short-circuiting the SSP code for sspstrong.

This check caused us to skip adding layout information for calls to
alloca in sspreq/sspstrong mode. We check properly for sspstrong later
on (and add the correct layout info when doing so), so removing this
shouldn't hurt.

No test is included, since testing this using lit seems to require
checking for exact offsets in asm, which is something that the lit tests
for this avoid. If someone cares deeply, I'm happy to write a unittest
or something to cover this, but that feels like overkill.

Patch by Daniel Micay.

Differential Revision: https://reviews.llvm.org/D22714

llvm-svn: 282022