COMP: Address greptile review on vendored Eigen 5 import

- Restore @EIGEN3_TARGETS_FILE@ substitution in Eigen3Config.cmake.in.
- Remove duplicate option(ITK_USE_EIGEN_MPL2_ONLY) declaration.
- Remove commented-out binary-dir generator expression.

USE_SYSTEM_EIGEN for 3.3+ unaffected (all under itkeigen, only
configured when USE_SYSTEM_EIGEN=OFF).

Author: hjmjohnson

Modules/ThirdParty/Eigen3/src/itkeigen/CMakeLists.txt

@@ -949,8 +949,7 @@ add_library (ITKInternalEigen3::Eigen ALIAS eigen_internal)
 # This would wrongly enforce EIGEN_MPL2_ONLY to other libraries using Eigen.
 # We wrap this definition in ITK_USE_EIGEN_MPL2_ONLY, and only enabling it internally in the dashboards and CI,
 # to avoid introducing GPL code from Eigen3 internally in ITK.
-option(ITK_USE_EIGEN_MPL2_ONLY "Set compile definition EIGEN_MPL2_ONLY for ITKInternalEigen3." OFF)
-mark_as_advanced(ITK_USE_EIGEN_MPL2_ONLY)
+# (ITK_USE_EIGEN_MPL2_ONLY is declared once near line 844 of this file.)
 
 if(ITK_USE_EIGEN_MPL2_ONLY)
   target_compile_definitions (eigen_internal INTERFACE "EIGEN_MPL2_ONLY")
@@ -961,7 +960,6 @@ endif()
 # INSTALL: headers require pre-prend itkeigen/Eigen/X.
 target_include_directories (eigen_internal SYSTEM INTERFACE
   $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/..>
-  # $<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR}/..>
   $<INSTALL_INTERFACE:${INCLUDE_INSTALL_DIR}>
   )
 

Modules/ThirdParty/Eigen3/src/itkeigen/cmake/Eigen3Config.cmake.in

@@ -4,5 +4,5 @@
 @PACKAGE_INIT@
 
 if (NOT TARGET Eigen3::Eigen)
-  include ("${CMAKE_CURRENT_LIST_DIR}/Eigen3Targets.cmake")
+  include ("${CMAKE_CURRENT_LIST_DIR}/@EIGEN3_TARGETS_FILE@")
 endif (NOT TARGET Eigen3::Eigen)