COMP: Drop the build-machine path from the installed vcl_where_root_dir.h

[hjmjohnson]

Advances the vendored VXL overlay past the removal of the vcl_where_root_dir mechanism. include/ITK-6.0/vcl_where_root_dir.h recorded the configuring machine's source directory and was installed, so every installed ITK published that path. With #6877 an install tree no longer references the machine that produced it.

Overlay change: InsightSoftwareConsortium/vxl for/itk-vxl-master-a0790d7.

Why the mechanism could be removed

VCL_SOURCE_ROOT_DIR had exactly one reader, testlib_root_dir(), and within the overlay the only callers of that function were its own tests, so it existed to test itself. ITK has no caller at all.

The 71 files that do call testlib_root_dir() in upstream vxl/vxl are all under contrib/, which the overlay does not carry. The removal is therefore overlay-only and is not proposed upstream.

vcl/CMakeLists.txt passed an install destination to vxl_configure_file, which is why the generated header was installed rather than staying in the build tree.

Verification

Measured against bare main rather than asserted, because the forest checkout has unrelated pre-existing failures.

Check	This branch	Bare main
ctest -R "vnl|VNL|testlib|vcl"	82/82 pass	—
Full build failures	16, all under Wrapping/	16, identical set
Broad-suite test failures	7	7, identical set
Build-log references to removed symbols	0	—

The 16 build failures and 7 test failures are name-for-name identical with and without this change, so none are attributable to it. They are stale remote-module wrapping breakage (VariationalRegistration, IsotropicWavelets, BoneMorphometry, IOMeshMZ3) plus RUNS_LONG registration tests on a loaded host.

Installed tree, with #6877 applied: no file references the build tree or the source tree.

pre-commit run --all-files exits 0.

Pin and topology

The subtree was imported with Modules/ThirdParty/VNL/UpdateFromUpstream.sh, so the history keeps the two-parent merge the ingest convention requires:

7dc5f87f985  COMP: Advance the VXL overlay pin past vcl_where_root_dir
d50fbf64095  Merge branch 'upstream-VXL'
69ccaea15e4  VXL 2026-09-20 (a0790d71)

The overlay commit was pushed directly to the fork as the new anchor rather than merged through a pull request there. Merging would have produced a merge commit with a different SHA, giving a second anchor candidate and invalidating this pin. Pushing directly keeps the overlay tip and the anchor the same object, matching the 7-character form the existing anchors use.

Depends on #6877 only for the combined result; the two changes are independent and can merge in either order.

[greptile-apps]

Confidence Score: 5/5

Safe to merge: no actionable issue was identified, and the removed mechanism has no remaining tracked references.

What we checked:

• Compared the baseline and updated VXL trees to focus on the removed root-directory mechanism.
• Confirmed that the baseline contains the expected references and that the updated tracked VXL files contain no remaining references or implementation paths.
• Captured and published artifacts including the shell script for the removed root-directory reference check and the baseline and updated reference-check logs.

Summary

This update advances the vendored VXL overlay and removes the obsolete source-root discovery mechanism. The removed header, testlib_root_dir implementation, registrations, and tests have no remaining tracked references.

T-Rex validation blocked

A full CMake configure, build, install, and test run could not be performed because cmake is unavailable in the environment; ctest and ninja are also unavailable.

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