Check if the given C++ source code compiles and runs.


<code>   - source code to try to compile
<var>    - variable to store the result
           (1 for success, empty for failure)

The following variables may be set before calling this macro to modify the way the check is run:

CMAKE_REQUIRED_FLAGS = string of compile command line flags
CMAKE_REQUIRED_DEFINITIONS = list of macros to define (-DFOO=bar)
CMAKE_REQUIRED_INCLUDES = list of include directories
CMAKE_REQUIRED_LIBRARIES = list of libraries to link