Move spack installation root inside build directory

Author: boomanaiden154

llvm_ir_dataset_utils/util/spack.py

@@ -51,6 +51,8 @@ def get_spack_compiler_config():
 
 def get_spack_config(build_dir):
   spack_config = ("config:\n"
+                  "  install_tree:\n"
+                  f"    root: {build_dir}/spack-installs\n"
                   "  build_stage:\n"
                   f"    - {build_dir}/build-stage\n"
                   f"  test_stage: {build_dir}/test-stage\n"