CMake/Modules/Platform/gcc.cmake

IF(CMAKE_COMPILER_IS_GNUCC)
  SET (CMAKE_C_FLAGS_INIT "")
  SET (CMAKE_C_FLAGS_DEBUG_INIT "-g")
  SET (CMAKE_C_FLAGS_MINSIZEREL_INIT "-Os -DNDEBUG")
  SET (CMAKE_C_FLAGS_RELEASE_INIT "-O3 -DNDEBUG")
  SET (CMAKE_C_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
ENDIF(CMAKE_COMPILER_IS_GNUCC)

IF(CMAKE_COMPILER_IS_GNUCXX)
  SET (CMAKE_CXX_FLAGS_INIT "")
  SET (CMAKE_CXX_FLAGS_DEBUG_INIT "-g")
  SET (CMAKE_CXX_FLAGS_MINSIZEREL_INIT "-Os -DNDEBUG")
  SET (CMAKE_CXX_FLAGS_RELEASE_INIT "-O3 -DNDEBUG")
  SET (CMAKE_CXX_FLAGS_RELWITHDEBINFO_INIT "-O2 -g")
ENDIF(CMAKE_COMPILER_IS_GNUCXX)