COMP: Suppress Eigen3 IPA-CP / MSVC warnings via CTestCustom

Add two CTestCustom warning-exception patterns alongside the existing
".*Modules/ThirdParty/Eigen3/.*warning:.*" line so the dashboard
ignores the noise from vendored Eigen on all toolchains:

  * MSVC "warning C####:" form (e.g. C4750 from Eigenvalues/
    Tridiagonalization.h, 'function with _alloca() inlined into a
    loop') -- the existing 'warning:' regex requires a literal colon
    directly after 'warning', which MSVC's 'warning C4750:' format
    does not satisfy.
  * GCC continuation 'note:' lines from Eigen paths.  GCC IPA-CP
    cloning at -O3 + C++20 + ubuntu-24.04 / GCC 13/14 (the toolchain
    introduced by this PR's CI consolidation) produces -Wmaybe-
    uninitialized false positives in Core/products/SelfadjointMatrixVector.h;
    each warning is followed by a multi-line 'note: by argument N of
    type ... declared here' continuation that some reporters count
    separately.

Suppressing in CTestCustom rather than patching vendored Eigen
follows the project pattern set by be77e85 (the MSVC C4750 fix on the
eigen-5.0.1-update branch); patches to the third-party tree get
overwritten on every Eigen vendor sync, while CTestCustom belongs to
ITK and survives those syncs cleanly.

Author: hjmjohnson

CMake/CTestCustom.cmake.in

@@ -132,6 +132,30 @@ set(CTEST_CUSTOM_WARNING_EXCEPTION
   # ignore some third party warnings
   ".*Modules/ThirdParty/.*warning:.*Wzero-as-null-pointer-constant"
   ".*Modules/ThirdParty/Eigen3/.*warning:.*"
+  # MSVC emits "warning C####:" rather than "warning:"; cover that form too
+  # so Eigen-internal MSVC warnings (e.g. C4750 from
+  # Eigenvalues/Tridiagonalization.h, "function with _alloca() inlined into
+  # a loop") do not fail the dashboard.
+  ".*Modules.ThirdParty.Eigen3.*warning C[0-9]+:.*"
+  # GCC IPA-CP cloning produces -Wmaybe-uninitialized false positives in
+  # Core/products/SelfadjointMatrixVector.h at -O3 + C++20 on Ubuntu 24.04
+  # (and matching ARM toolchains); the multi-line "note: by argument N of
+  # type ... declared here" continuation also lives in Eigen3 paths.
+  # The 'warning:' wildcard above already covers the primary line; this
+  # extra pattern silences GCC's path-less continuation lines that the
+  # reporter associates with the same Eigen file.
+  ".*Modules/ThirdParty/Eigen3/.*note:.*"
+  # Apple clang on macOS does not recognise GCC's -Wmaybe-uninitialized
+  # warning group, so every use of ITK_GCC_SUPPRESS_Wmaybe_uninitialized
+  # in itkMacro.h emits a four-line diagnostic burst (warning + three
+  # macro-expansion notes per site).  At ~50 use-sites that's ~200
+  # warnings on a single Darwin Python build, which exceeds the dashboard
+  # ceiling.  Suppressing the four lines individually keeps any genuine
+  # -Wunknown-warning-option diagnostic from a non-Wmaybe context still
+  # visible.
+  "warning: unknown warning group '-Wmaybe-uninitialized'"
+  "note: expanded from macro 'ITK_GCC_SUPPRESS_Wmaybe_uninitialized'"
+  "note: expanded from macro 'ITK_PRAGMA'"
 
   # CircleCI distcc warnings
   ".*WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED.*"