COMP: Build in-scope DCMTK alongside MINC on MSVC

Building DCMTK in ITK's shared CMake scope (FetchContent + add_subdirectory)
runs DCMTK's CHECK_*_EXISTS probes in that scope, with two effects on
sibling third-party modules:

- Leftover CMAKE_REQUIRED_* state from DCMTK's probes. Snapshot and restore
  it around FetchContent_MakeAvailable(dcmtk).

- DCMTK caches HAVE_TMPNAM=0 on MSVC (its tmpnam probe, like MINC's, uses
  CHECK_FUNCTION_EXISTS, which cannot detect MSVC CRT functions). MINC then
  inherits the cached 0 and its config.h selects none of mkstemp/tempnam/
  tmpnam, tripping the "System defines neither ..." #error. tmpnam() does
  exist in the MSVC CRT, so assert HAVE_TMPNAM directly for MSVC (matching
  MINC's own config.h.msvc-win32); the local set() also overrides any value
  left in the shared cache.

Author: hjmjohnson

Modules/ThirdParty/DCMTK/CMakeLists.txt

@@ -267,8 +267,30 @@ else(ITK_USE_SYSTEM_DCMTK)
     GIT_REPOSITORY ${DCMTK_GIT_REPOSITORY}
     GIT_TAG ${DCMTK_GIT_TAG}
   )
+
+  # DCMTK's configure runs many CHECK_*_EXISTS probes that mutate the shared
+  # CMAKE_REQUIRED_* state; in ITK's in-scope build that would leak into
+  # sibling third-party feature probes, so snapshot and restore it.
+  set(
+    _dcmtk_required_vars
+    CMAKE_REQUIRED_FLAGS
+    CMAKE_REQUIRED_DEFINITIONS
+    CMAKE_REQUIRED_INCLUDES
+    CMAKE_REQUIRED_LIBRARIES
+    CMAKE_REQUIRED_QUIET
+  )
+  foreach(_v ${_dcmtk_required_vars})
+    set(_dcmtk_saved_${_v} "${${_v}}")
+  endforeach()
+
   FetchContent_MakeAvailable(dcmtk)
 
+  foreach(_v ${_dcmtk_required_vars})
+    set(${_v} "${_dcmtk_saved_${_v}}")
+    unset(_dcmtk_saved_${_v})
+  endforeach()
+  unset(_dcmtk_required_vars)
+
   # Expose DCMTK's now-in-scope targets to the rest of ITK.
   set(ITKDCMTK_LIBRARIES ${_ITKDCMTK_LIB_NAMES})
   foreach(lib ${_ITKDCMTK_LIB_NAMES})

Modules/ThirdParty/MINC/src/libminc/CMakeLists.txt

@@ -142,6 +142,14 @@ CHECK_FUNCTION_EXISTS(strerror HAVE_STRERROR)
 CHECK_FUNCTION_EXISTS(sysconf  HAVE_SYSCONF)
 CHECK_FUNCTION_EXISTS(system   HAVE_SYSTEM)
 
+# tmpnam() is in the MSVC CRT but CHECK_FUNCTION_EXISTS cannot detect it (its
+# self-declared prototype fails to link); assert it directly so config.h picks
+# the tmpnam path rather than tripping the no-temp-file #error. A local set()
+# also overrides any HAVE_TMPNAM left in the shared cache by a sibling build.
+if(MSVC)
+  set(HAVE_TMPNAM 1)
+endif()
+
 if(NOT MSVC)
   set(CMAKE_REQUIRED_LIBRARIES m)
 endif()