Add --disable-optimizations and update TODO...

Please note that --enable-optimizations is by default yes and, at least in
pkgsrc, should not be:
 1. usually the user should decide her favourite CFLAGS
 2. --enable-optimizations also add -D_FORTIFY_SOURCE=2 without including
 -I/usr/include/ssp nor passing to the linker -lssp (seems)
The (2) is more critical and you can reproduce it, at least with lang/gcc48,
adding --enable-optimizations and watching that webkit-gtk will fail in the
configure phase when checking for pthread... Then please see the config.log
and you will find an error about <ssp.h>.

XXX: I am trying again to build it. THIS IS STILL EXPERIMENTAL!