Cut VectorizationBase into pieces

[chriselrod]

The goal of this is to improve compile and load times.
It also would be nice for libraries wanting to take on smaller dependencies.

Additionally, LoopVectorization itself might no longer depend on llvmcall at all in the future, but may still want other parts.

The pieces:

• LLVMCalls
• Hardware info
• StridedPointers
• VectorizationBase

[timholy]

Let me know if you need some help. In the meantime my goal is to start learning more about why precompile sometimes fails (beyond the reasons I already know about, all of which except one---constprop---have a workaround).

[chriselrod]

Help is always welcome, but not sure what anyone is willing/eager to do.

Currently one 3/2 steps remain: removing the llvmcalls (unchecked), and finish updating packages for a few other breakages.
I'll probably start working on Octavian and dependents next week.