[te] Get llvm codegen to compile with llvm9 and llvm-fb (#45726)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/45726
FB has an old internal platform that uses some random llvm version
that looks sort of like llvm 7. I've guarded that with the appropriate
LLVM_VERSION_PATCH.
I've also swapped out some of our uses of ThreadSafeModule/ThreadSafeContext
for the variants without ThreadSafe in the name. As far as I can tell we
weren't using the bundled locks anyways, but I'm like 85% sure this is OK since
we compile under the Torch JIT lock anyways.
Test Plan: unit tests
Reviewed By: ZolotukhinM, asuhan
Differential Revision: D24072697
fbshipit-source-id: 7f56b9f3cbe5e6d54416acdf73876338df69ddb2
