There are some more options that can be set with special variables. In general they are simply shortcuts and can be replaced with adding compiler command-line options to OPT:
LINKSMART=1
adds -XX to the compiler command-line options.
CREATESMART=1
adds -CX to the compiler command-line options.
DEBUG=1
adds -gl and -dDEBUG to the compiler command-line options.
RELEASE=1
adds -O1r or -O2 depending on the CPU, and -Ur and -DRELAASE to the command-line.
STRIP=1
adds -Xs to the command-line.
OPTIMIZE=1
adds -O2 to the command-line.
VERBOSE=1
adds -vwni to the command-line.