[TensorExpr] Support LLVM versions 8 through 12 (#47033)
Summary:
Adjust llvm_{codegen, jit}.cpp to support LLVM versions 8 through 12.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47033
Test Plan: test_tensorexpr --gtest_filter=TensorExprTest.LLVM*
Reviewed By: bertmaher
Differential Revision: D24689903
Pulled By: asuhan
fbshipit-source-id: 2654bb7eb2ab6a95a5527c079b07ed8552c51bde
