If you have CMake code using check_symbol_exists(...)
like
list(APPEND CMAKE_REQUIRED_LIBRARIES m) check_symbol_exists(atan2 math.h HAVE_ATAN2)
but you get an error message like
CMake Error at CMakeLists.txt:8 (check_symbol_exists): Unknown CMake command "check_symbol_exists". -- Configuring incomplete, errors occurred!
you need to add
include(CheckSymbolExists)
near the top of your CMakeLists.txt
(before your first call to check_symbol_exists()
).