If we are using the Apple toolchain on MacOS X, we must use the
newer runtime and not the old GCC 4.2 fork, in order to get the
C++11 library features (such as std::shared_ptr).
v2: incorporate Roland's nitpicks (I hope)
v3: It was decided that it's better to change the default behavior
v4: make sure the CMake syntax is correct even if the value of the
variable contains spaces (if it contains double quotes it's a
different matter, but that's pretty much a corner case, IMHO)
v5: properly escape backslash and double quote characters in the cmake
syntax
CMAKE_REQUIRED_FLAGS is intended to be added only to the compile for the
next probe, and inside an cmake_push_check_state/cmake_pop_check_state
guard. If we add it to the main flags (CMAKE_CXX_FLAGS), it will also be
added to subsequent checks, so it suffices.
We want to compile with the -std=c++0x since DUNE uses this settings and
we need to use the same ABI as that one if we are going to link with it.
Find module is a copy of the one in cmake/modules in (the cmake branch of)
dune-common.
