CGAL test does not honor linker flags

[Yaakoub El Khamra]

the FindCGAL.cmake module tries to compile and link a CGAL test code. The code is linked against ${CMAKE_REQUIRED_LIBRARIES} and ${Boost_LIBRARIES}. It does not honor any linker flags set by the user. An easy work around is to append ${CMAKE_EXE_LINKER_FLAGS} to the list of of required libraries. The following is the resulting diff on the affected file: cmake/modules/FindCGAL.cmake

- set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} ${Boost_LIBRARIES})
+ set(CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES} ${Boost_LIBRARIES} ${CMAKE_EXE_LINKER_FLAGS})

I tested this and it works, but there might be a more elegant way of doing this, one that adds the linker flags to all modules where test code is compiled and linked. Anyways, current patch attached.

Regards
Yaakoub