Sometimes the command lines that SCons executes don't come out looking as you expect. In this case it may be useful to look at the strings before SCons performs substitution on them. This can be done with the --debug=presub option:

% scons -Q --debug=presub
Building prog.o with action:
  $CC -o $TARGET -c $CFLAGS $CCFLAGS $_CCOMCOM $SOURCES
cc -o prog.o -c -I. prog.c
Building prog with action:
  $SMART_LINKCOM
cc -o prog prog.o