COMP: compile without FFTW to avoid GPL contamination

Close #2454 (closed) . To avoid the GPL contamination inside OTB, do not compile ITK with FFTW. Instead let the fftw compilation disabled by defaut and if the user want to compile with it, inform it with a cmake message that the otb compiled relies on GNU GPL v2 license instead of Apache 2.

So by default:

• skip the fftw downloading and compilation
• do not use ITK fftw options
• do not compile and add OverlapSaveConvolutionImageFilter inside the package
• Do not compile tests relying on OverlapSaveConvolutionImageFilter

The cmake option OTB_USE_FFTW=ON should change this behavior to the actual one and emit a message explaining the license change.

CI/FFTW_tests.cmake

+#
+# Copyright (C) 2005-2024 Centre National d'Etudes Spatiales (CNES)
+#
+# This file is part of Orfeo Toolbox
+#
+#     https://www.orfeo-toolbox.org/
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+include( "${CMAKE_CURRENT_LIST_DIR}/macros.cmake" )
+get_filename_component(OTB_SOURCE_DIR ${CMAKE_CURRENT_LIST_DIR} DIRECTORY)
+set (ENV{LANG} "C") # Only ascii output
+
+# Build Configuration : Release, Debug..
+if(ci_build_type)
+  set (CTEST_BUILD_CONFIGURATION ${ci_build_type})
+else()
+  set (CTEST_BUILD_CONFIGURATION "Release")
+endif()
+
+set (CTEST_CMAKE_GENERATOR "Ninja")
+
+# detect short sha
+if(NOT DEFINED ENV{CI_COMMIT_SHORT_SHA})
+  execute_process(COMMAND git log -1 --pretty=format:%h
+                  WORKING_DIRECTORY ${OTB_SOURCE_DIR}
+                  OUTPUT_VARIABLE ci_short_sha)
+else()
+  set(ci_short_sha "$ENV{CI_COMMIT_SHORT_SHA}")
+endif()
+
+# Find the build name and CI profile. Customize it with FFTW
+set_dash_build_name()
+set (CTEST_BUILD_NAME "FFTW Tests ${ci_ref_name} P-${ci_pipeline_id}")
+
+# Detect site
+if(NOT DEFINED IMAGE_NAME)
+  if(DEFINED ENV{IMAGE_NAME})
+    set(IMAGE_NAME $ENV{IMAGE_NAME})
+  endif()
+endif()
+set (CTEST_SITE "${IMAGE_NAME}")
+
+# Directory variable
+set (CTEST_SOURCE_DIRECTORY "${OTB_SOURCE_DIR}")
+if(BUILD_DIR)
+  set (CTEST_BINARY_DIRECTORY "${BUILD_DIR}")
+else()
+  set (CTEST_BINARY_DIRECTORY "${OTB_SOURCE_DIR}/build/")
+endif()
+set (CTEST_INSTALL_DIRECTORY "${OTB_SOURCE_DIR}/install/")
+set (PROJECT_SOURCE_DIR "${OTB_SOURCE_DIR}")
+
+# Ctest command value
+set (CMAKE_COMMAND "cmake")
+
+message(STATUS "CI profile : ${ci_profile}")
+
+# Sources are already checked out : do nothing for update
+set(CTEST_GIT_UPDATE_CUSTOM "${CMAKE_COMMAND}" "-E" "echo" "No update")
+# Look for a GIT command-line client.
+find_program(CTEST_GIT_COMMAND NAMES git git.cmd)
+
+
+
+ctest_start (Experimental TRACK CI_Build)
+
+ctest_update()
+
+# Run only onverlapSave tests
+ctest_test(PARALLEL_LEVEL 8
+    RETURN_VALUE _test_rv
+    CAPTURE_CMAKE_ERROR _test_error
+    INCLUDE "OverlapSave"
+    )
+  # Test log
+file ( WRITE 
+"${OTB_SOURCE_DIR}/log/test_return_value_log.txt" "${_test_rv}")
+file ( WRITE 
+"${OTB_SOURCE_DIR}/log/test_cmake_error_log.txt" "${_test_error}")
+
+if ( NOT _test_rv EQUAL 0 )
+  message( SEND_ERROR "An error occurs during ctest_test.")
+endif()
+
+ctest_submit()