Revert "[CI] Disable LTC build from CI (#3911)"

This reverts commit c253512.

Author: rahuls-cerebras

build_tools/ci/build_posix.sh

@@ -50,7 +50,7 @@ cmake -S "$repo_root/externals/llvm-project/llvm" -B "$build_dir" \
   -DLLVM_EXTERNAL_TORCH_MLIR_SOURCE_DIR="$repo_root" \
   -DLLVM_TARGETS_TO_BUILD=host \
   -DMLIR_ENABLE_BINDINGS_PYTHON=ON \
-  -DTORCH_MLIR_ENABLE_LTC=OFF \
+  -DTORCH_MLIR_ENABLE_LTC=ON \
   -DTORCH_MLIR_ENABLE_PYTORCH_EXTENSIONS=ON
 echo "::endgroup::"