issue finding HIP

I am trying to build `umpire+rocm` in a larger spack env and running into HIP configure issues that I suspect are related to BLT (this is the only project building with it in the env). I have in my packages.py:

```
umpire:
require: '%[when=%c] c=rocmcc %[when=%cxx] cxx=rocmcc %[when=%fortran] fortran=gcc amdgpu_target=gfx942'
```
where rocmcc is pulling in an externally installed rocm.

In the concretization, I see

```
umpire@4.1.2~asan~backtrace+c~cuda~dev_benchmarks~device_alloc~deviceconst~examples+fmt_header_only~fortran~ipc_shmem~ipo~mpi~mpi3_shmem~numa~omptarget~openmp+rocm~sanitizer_tests+shared~sqlite_experimental~tools~werror amdgpu_target:=gfx942 build_system=cmake build_type=Release commit=447f4640eff7b8f39d3c59404f3b03629b90c021 generator=make patches:=135bbc7,7d912d3,f3b2133 tests=none platform=linux os=rhel8 target=zen4 %fortran=gcc@13.3.1 %c,cxx=rocmcc@19.0.0
[+] vn72bsg ^blt@0.4.1 build_system=generic platform=linux os=rhel8 target=zen4 %fortran=gcc@13.3.1 %c,cxx=rocmcc@19.0.0
```
which seems like what I would expect. However, when trying to configure umpire, I get

```
1 error found in build log:
50 -- Git Executable: /usr/tce/bin/git
51 -- Git Version: 2.29.1
52 -- MPI Support is OFF
53 -- OpenMP Support is OFF
54 -- CUDA Support is OFF
55 -- HIP Support is ON
>> 56 CMake Error at /usr/gapps/user_contrib/capsaicin_modules/spack-environments.20260302/ATS4G_GPU/3.0.1/spack/opt/spack/linux-zen4
/blt-0.4.1-vn72bsg/cmake/thirdparty/FindHIP.cmake:58 (message):
57 Specify HIP_ROOT_DIR
58 Call Stack (most recent call first):
59 /usr/gapps/user_contrib/capsaicin_modules/spack-environments.20260302/ATS4G_GPU/3.0.1/spack/opt/spack/linux-zen4/blt-0.4.1-vn
72bsg/cmake/thirdparty/SetupHIP.cmake:13 (find_package)
60 /usr/gapps/user_contrib/capsaicin_modules/spack-environments.20260302/ATS4G_GPU/3.0.1/spack/opt/spack/linux-zen4/blt-0.4.1-vn
72bsg/cmake/thirdparty/SetupThirdParty.cmake:56 (include)
61 /usr/gapps/user_contrib/capsaicin_modules/spack-environments.20260302/ATS4G_GPU/3.0.1/spack/opt/spack/linux-zen4/blt-0.4.1-vn
72bsg/SetupBLT.cmake:112 (include)
62 CMakeLists.txt:120 (include)
```
What might I be missing here, or is there some other secret sauce I'm missing to build this?

Start with cmake/thirdparty/FindHIP.cmake and follow its call path through SetupHIP.cmake, SetupThirdParty.cmake, SetupBLT.cmake, and CMakeLists.txt at line 120. Reproduce the Umpire ROCm configuration and inspect how HIP_ROOT_DIR is discovered or passed. Done means the HIP-enabled configuration completes without the Specify HIP_ROOT_DIR error.

Written by the indexing model from the issue text.