BUG: Drop build-machine paths from the installed gdcmConfigure.h

[hjmjohnson]

An installed ITK carried the build machine's source and output directories in the public header include/ITK-6.0/gdcmConfigure.h, two of them holding an unevaluated generator expression. Dropping the three macros leaves an install tree with no reference to the machine that produced it. Fixes #6876.

What the installed header contained

#define GDCM_SOURCE_DIR "/home/<user>/src/ITK/Modules/ThirdParty/GDCM/src/gdcm"
#define GDCM_EXECUTABLE_OUTPUT_PATH "$<1:/home/<user>/build/Wrapping/Generators/Python/itk>"
#define GDCM_LIBRARY_OUTPUT_PATH    "$<1:/home/<user>/build/Wrapping/Generators/Python/itk>"

CMake/WrappingConfigCommon.cmake wraps the output directory in a generator expression so multi-config generators do not append a per-config subdirectory. configure_file does not evaluate generator expressions, so $<1:...> reached the installed header as literal text and the last two macros did not name a real directory on any machine.

Why removing them is safe

GDCM_EXECUTABLE_OUTPUT_PATH and GDCM_LIBRARY_OUTPUT_PATH have no reference anywhere outside the template that defines them.

GDCM_SOURCE_DIR does have consumers, so the reason it can go is different: gdcmTesting.cxx is added to the source list only under if(GDCM_BUILD_TESTING), and the GDCM_SOURCE_DIR use in gdcmGlobal.cxx sits inside #ifdef GDCM_BUILD_TESTING. Modules/ThirdParty/GDCM/src/gdcm/CMakeLists.txt:495 sets GDCM_BUILD_TESTING OFF for a non-standalone GDCM, which is always ITK's case, so neither consumer is ever compiled here.

This patches vendored third-party source, as 4aec5d1 did for this same file.

Verification

Measured on a real install rather than by inspection.

Check	Before	After
Install files referencing the build tree	include/ITK-6.0/gdcmConfigure.h	none
GDCM_* path macros in the installed header	3	0

cmake --install <build> --prefix /tmp/itk-verify-prefix
grep -rl "<build>" /tmp/itk-verify-prefix     # no output

• ctest -R "GDCM|gdcm" — 103/103 passed.
• gdcmCommon, gdcmDICT, gdcmDSED, gdcmMSFF, ITKIOGDCM rebuilt: 0 warnings, 0 errors.
• pre-commit run --all-files — exit 0.

Remaining, not addressed here

After this change include/ITK-6.0/vcl_where_root_dir.h is the only file in a clean install that names a path on the build machine, via VCL_SOURCE_ROOT_DIR. It is a separate concern in vendored VXL with a different shape, since its consumer is compiled unconditionally, and it belongs in its own change against the VXL fork.

[greptile-apps]

Confidence Score: 5/5

Safe to merge.

Summary

The GDCM configuration template keeps the upstream path macro definitions in a clearly marked, inactive ITK block. The generated header therefore does not expose build-machine source or output paths while retaining upstream context for future synchronization.

_{Reviews (2) · Last reviewed commit: "BUG: Drop build-machine paths from the i..."}

[hjmjohnson]

@greptileai please re-review — the patch now keeps the upstream lines under #if 0 inside a BEGIN ITK / END ITK block rather than replacing them; the prior review covered e8c3886.