build: add SUNDIALS as git submodule (neuronsimulator fork)

- Add external/sundials submodule pointing to neuronsimulator/sundials (hines/hoc_pow)
- Update FindSUNDIALS.cmake to use the standard submodule approach.
- Build SUNDIALS inside the main build directory.
- Initialization consistent with other submodules (InterViews, etc.)

Author: nrnhines

.gitmodules

@@ -37,3 +37,7 @@
 [submodule "external/spdlog"]
 	path = external/spdlog
 	url = https://github.com/gabime/spdlog.git
+[submodule "external/sundials"]
+	path = external/sundials
+	url = https://github.com/neuronsimulator/sundials.git
+	branch = hines/hoc_pow

cmake/modules/FindSUNDIALS.cmake

@@ -1,58 +1,54 @@
-# =============================================================================
-# Sundials
-# =============================================================================
+# cmake/modules/FindSUNDIALS.cmake
 
-include(ExternalProject)
-set(SUNDIALS_PREFIX "${THIRD_PARTY_DIRECTORY}/sundials")
+set(SUNDIALS_SOURCE_DIR "${PROJECT_SOURCE_DIR}/external/sundials")
+
+# Use the same pattern as other submodules in NEURON
+if(NOT EXISTS "${SUNDIALS_SOURCE_DIR}/CMakeLists.txt")
+  message(STATUS "SUNDIALS submodule not found.")
+  include(${PROJECT_SOURCE_DIR}/cmake/ExternalProjectHelper.cmake)
+  nrn_initialize_submodule(external/sundials)
+endif()
+
+if(NOT EXISTS "${SUNDIALS_SOURCE_DIR}/CMakeLists.txt")
+  message(FATAL_ERROR "Failed to initialize SUNDIALS submodule")
+endif()
+
+set(SUNDIALS_PREFIX "${CMAKE_BINARY_DIR}/external/sundials")
 set(SUNDIALS_INCLUDE_DIR "${SUNDIALS_PREFIX}/include")
 set(SUNDIALS_LIB_DIR "${SUNDIALS_PREFIX}/lib")
-make_directory(${SUNDIALS_INCLUDE_DIR})
 
-set(SUNDIALS_C_FLAGS ${CMAKE_C_FLAGS})
-list(REMOVE_ITEM SUNDIALS_C_FLAGS "-tp=haswell")
-set(SUNDIALS_CXX_FLAGS ${CMAKE_CXX_FLAGS})
-list(REMOVE_ITEM SUNDIALS_CXX_FLAGS "-tp=haswell")
 include(ExternalProject)
 ExternalProject_Add(
-  sundials-external
+  sundials
+  SOURCE_DIR "${SUNDIALS_SOURCE_DIR}"
   PREFIX "${SUNDIALS_PREFIX}"
-  # cmake-format: off
-  # GIT_REPOSITORY https://github.com/LLNL/sundials.git
-  # Forked to following, to allow RPowerR to use hoc_pow
-  GIT_REPOSITORY https://github.com/neuronsimulator/sundials.git
-  # GIT_TAG e2f29c34f324829302037a1492db480be8828084   6.2.0 -> CVodeMem no longer "visible" GIT_TAG
-  # c09e732080a214694b209032ec627c93fed45340  4
-  #GIT_TAG 811234254d37652954daff0ccdb7af9813736846 # 3.2.1
-  GIT_TAG 71b3daec18ce66a7c011be9501a31567aa5c09b6 # 3.2.1 hines/hoc_pow
-  # GIT_TAG 7ed895fd102226dbc52225e6b2c6e26ef1cafa0e  #2.7.0
-  # cmake-format: on
-  GIT_SHALLOW ON
-  GIT_PROGRESS ON
-  # UPDATE_COMMAND ""
   CMAKE_ARGS -DCMAKE_INSTALL_PREFIX=<INSTALL_DIR>
              -DCMAKE_C_COMPILER=${CMAKE_C_COMPILER}
              -DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}
-             -DCMAKE_C_FLAGS=${SUNDIALS_C_FLAGS}
-             -DCMAKE_CXX_FLAGS=${SUNDIALS_CXX_FLAGS}
              -DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}
+             -DCMAKE_POSITION_INDEPENDENT_CODE=ON
+             -DBUILD_SHARED_LIBS=OFF
+             -DEXAMPLES_ENABLE_C=OFF
              -DEXAMPLES_INSTALL=OFF
              -DBUILD_ARKODE=OFF
              -DBUILD_CVODES=OFF
              -DBUILD_IDAS=OFF
              -DBUILD_KINSOL=OFF
-             -DEXAMPLES_ENABLE_C=OFF
              -DMPI_ENABLE=OFF
              -DPTHREAD_ENABLE=ON
              -DSUNDIALS_PRECISION=double
              -DUSE_GENERIC_MATH=ON
-             -DCMAKE_POSITION_INDEPENDENT_CODE=ON
-             -DBUILD_SHARED_LIBS=OFF
-             -DMPI_C_COMPILER=${MPI_C_COMPILER}
-             -DCMAKE_INSTALL_LIBDIR=${SUNDIALS_LIB_DIR}
   BUILD_BYPRODUCTS
-    <INSTALL_DIR>/lib/libsundials_ida.a <INSTALL_DIR>/lib/libsundials_cvode.a
+    <INSTALL_DIR>/lib/libsundials_cvode.a <INSTALL_DIR>/lib/libsundials_ida.a
     <INSTALL_DIR>/lib/libsundials_nvecserial.a <INSTALL_DIR>/lib/libsundials_nvecpthreads.a
-    <INSTALL_DIR>/lib/libsundials_nvecparallel.a)
+  INSTALL_DIR "${SUNDIALS_PREFIX}")
 
 add_library(SUNDIALS INTERFACE IMPORTED)
-add_dependencies(SUNDIALS sundials-external)
+add_dependencies(SUNDIALS sundials)
+
+set(SUNDIALS_INCLUDE_DIR
+    "${SUNDIALS_INCLUDE_DIR}"
+    PARENT_SCOPE)
+set(SUNDIALS_LIB_DIR
+    "${SUNDIALS_LIB_DIR}"
+    PARENT_SCOPE)