You almost have it right; why did you add the semicolon?
To do it on the configure line:
./configure CFLAGS='-g -O2 -w' CXXFLAGS='-g -O2 -w'
To do it on the make line:
make CFLAGS='-g -O2 -w' CXXFLAGS='-g -O2 -w'
However, that doesn’t really remove consider all warnings as errors; that removes all warnings. So specifying both -Wall and -w doesn’t make sense. If you want to keep the warnings but not have them considered errors, use the -Wall -Wno-error flags.
Alternatively, most configure scripts which enable -Werror by default also have a flag such as --disable-werror or similar. Run ./configure --help and see if there’s something like that.