[IR] Add a few asserts to provide a better failure signature if you try to...

[IR] Add a few asserts to provide a better failure signature if you try to create a load/store/alloca with no alignment or insertion position

If no alignment is specified we try to find the datalayout by using the insert position to get the module so we can get the datalayout. But if those are null, then we deference a null pointer.

This patch adds asserts to make the failure a little more obvious than just seg faulting.

Differential Revision: https://reviews.llvm.org/D83829