Each of these options may be passed multiple times. The advantage over
the previous interface (environment variables SG_CMAKEARGS and
FG_CMAKEARGS) is that the new interface allows one to pass arguments
containing spaces to CMake, for instance:
--sg-cmake-args='-DCMAKE_CXX_FLAGS=-Wno-deprecated-declarations -Wall'
(the single quotes here would be interpreted by the user's shell, and
removed before download_and_compile.sh can see them). Setting the
environment variables SG_CMAKEARGS and FG_CMAKEARGS should still work as
before but is now deprecated.
The implementation uses Bash arrays named SG_CMAKE_ARGS and
FG_CMAKE_ARGS, but in order to avoid confusing users about the
deprecated variable names, the log file continues to print
'SG_CMAKEARGS=...' and 'FG_CMAKEARGS=...' (note the different use of
underscores in the names).