[llvm][oncall] Fix build for llvm-18+ (pytorch#115652)

Summary:
https://reviews.llvm.org/D137838 moved Host.h and some other files under TargetParser.
llvm/llvm-project#74261 Removed it from Support folder.

Pull Request resolved: pytorch#115652
Approved by: https://github.com/davidberard98

Author: ayermolo