Check if a C function can be linked

CHECK_FUNCTION_EXISTS(<function> <variable>)

Check that the <function> is provided by libraries on the system and store the result in a <variable>. This does not verify that any system header file declares the function, only that it can be found at link time (consider using CheckSymbolExists).

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