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). <variable> will be created as an internal cache variable.

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
CMAKE_REQUIRED_QUIET = execute quietly without messages