[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

torch/csrc/jit/tensorexpr/llvm_codegen.cpp

@@ -35,7 +35,11 @@
 #include <llvm/Passes/PassBuilder.h>
 #pragma GCC diagnostic pop
 
+#if LLVM_VERSION_MAJOR >= 18
+#include <llvm/TargetParser/Host.h>
+#else
 #include <llvm/Support/Host.h>
+#endif
 #include <llvm/Support/TargetSelect.h>
 #include <llvm/Transforms/IPO/AlwaysInliner.h>
 #include <llvm/Transforms/Scalar/DCE.h>

torch/csrc/jit/tensorexpr/llvm_jit.cpp

@@ -28,7 +28,11 @@ C10_DIAGNOSTIC_POP()
 #include <llvm/IR/Mangler.h>
 #include <llvm/Support/CFGUpdate.h>
 #include <llvm/Support/DynamicLibrary.h>
+#if LLVM_VERSION_MAJOR >= 18
+#include <llvm/TargetParser/Host.h>
+#else
 #include <llvm/Support/Host.h>
+#endif
 #include <llvm/Support/raw_ostream.h>
 #include <llvm/Target/TargetMachine.h>