COMP: Suppress GCC -Wmaybe-uninitialized in Eigen3 SelfadjointMatrixVector

GCC on aarch64 (ARM) emits a false-positive -Wmaybe-uninitialized
warning at line 224 of SelfadjointMatrixVector.h. The dashboard script
(itk_common.cmake) treats any build warning as CI failure.

Add targeted GCC diagnostic pragmas to suppress the warning in this
file only, scoped to GCC (not Clang) via __GNUC__ / __clang__ guards.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: hjmjohnson

Modules/ThirdParty/Eigen3/src/itkeigen/Eigen/src/Core/products/SelfadjointMatrixVector.h

@@ -13,6 +13,13 @@
 // IWYU pragma: private
 #include "../InternalHeaderCheck.h"
 
+// GCC on ARM (aarch64) emits false-positive -Wmaybe-uninitialized warnings
+// in the vectorized selfadjoint matrix-vector product kernel.
+#if defined(__GNUC__) && !defined(__clang__)
+#  pragma GCC diagnostic push
+#  pragma GCC diagnostic ignored "-Wmaybe-uninitialized"
+#endif
+
 namespace Eigen {
 
 namespace internal {
@@ -250,4 +257,8 @@ struct selfadjoint_product_impl<Lhs, 0, true, Rhs, RhsMode, false> {
 
 }  // end namespace Eigen
 
+#if defined(__GNUC__) && !defined(__clang__)
+#  pragma GCC diagnostic pop
+#endif
+
 #endif  // EIGEN_SELFADJOINT_MATRIX_VECTOR_H