[cmake] pcl_options.cmake modified CMAKE_FIND_LIBRARY_SUFFIXES, resulting in failure to find dependencies

[JackBoosY]

Hi guys,
I'm vcpkg maintainer.
Recently we are updating pcl in vcpkg (microsoft/vcpkg#18855), but met some problems:
When vtk, a dependency of pcl, finds qt, an error occurs:

CMake Error at /mnt/vcpkg-ci/installed/x64-linux/share/cmake/Qt5Gui/Qt5GuiConfig.cmake:95 (message):
  Library not found: GL
Call Stack (most recent call first):
  /mnt/vcpkg-ci/installed/x64-linux/share/cmake/Qt5Gui/Qt5GuiConfig.cmake:277 (_qt5_Gui_process_prl_file)
  /agent/_work/1/s/scripts/buildsystems/vcpkg.cmake:792 (_find_package)
  /mnt/vcpkg-ci/installed/x64-linux/share/cmake/Qt5Widgets/Qt5WidgetsConfig.cmake:231 (find_package)
  /agent/_work/1/s/scripts/buildsystems/vcpkg.cmake:792 (_find_package)
  /mnt/vcpkg-ci/installed/x64-linux/share/cmake/Qt5/Qt5Config.cmake:28 (find_package)
  /agent/_work/1/s/scripts/buildsystems/vcpkg.cmake:792 (_find_package)
  /mnt/vcpkg-ci/installed/x64-linux/share/vtk/VTK-vtk-module-find-packages.cmake:115 (find_package)
  /mnt/vcpkg-ci/installed/x64-linux/share/vtk/vtk-config.cmake:129 (include)
  /agent/_work/1/s/scripts/buildsystems/vcpkg.cmake:792 (_find_package)
  cmake/pcl_find_vtk.cmake:25 (find_package)
  CMakeLists.txt:380 (include)

After a long period of searching, we found that pcl modified the value of CMAKE_FIND_LIBRARY_SUFFIXES in pcl_options.cmake, which caused its downstream dependencies to fail to find their dependencies through find_library.
For example, qt needs libGL.so, and CMAKE_FIND_LIBRARY_SUFFIXES is modified to .a when statically building PCL, which results in find_library expecting to find libGL.a.
See code:

pcl/cmake/pcl_options.cmake

Lines 5 to 18 in cd99687

	if(PCL_SHARED_LIBS)
	set(PCL_LIB_PREFIX ${CMAKE_SHARED_LIBRARY_PREFIX})
	set(PCL_LIB_SUFFIX ${CMAKE_SHARED_LIBRARY_SUFFIX})
	set(PCL_LIB_TYPE "SHARED")
	# set(CMAKE_FIND_LIBRARY_SUFFIXES ${CMAKE_SHARED_LIBRARY_SUFFIX})
	if(WIN32)
	set(CMAKE_FIND_LIBRARY_SUFFIXES ${CMAKE_IMPORT_LIBRARY_SUFFIX})
	endif()
	else()
	set(PCL_LIB_PREFIX ${CMAKE_STATIC_LIBRARY_PREFIX})
	set(PCL_LIB_SUFFIX ${CMAKE_STATIC_LIBRARY_SUFFIX})
	set(PCL_LIB_TYPE "STATIC")
	set(CMAKE_FIND_LIBRARY_SUFFIXES ${CMAKE_STATIC_LIBRARY_SUFFIX})
	endif()

So, please DO NOT do that, any modification of the cmake macro value that has not been backed up and restored will cause errors when using the downstream configuration.

Thanks,
Jack

[JackBoosY]

Maybe related PR: #4390