+if( DEFINED OPT_LEVEL )
+ message( "+++ optimisation is forced to ${OPT_LEVEL}" )
+ set( CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -O${OPT_LEVEL} " )
+else()
+ message( "+++ optimisation will default (use -DOPT_LEVEL=n to force specific level, or disable)" )
+endif()
+unset( OPT_LEVEL CACHE ) # no optimisation flage does NOT percist
+
+message( "+++ compiler flags: ${CMAKE_C_FLAGS}" )
+
+