Put together an initial run at a config.h-style configuration, rather
than piling up -D's on the command line.
Make sure ctwm.h is pulled into all our C files.
Make sure ctwm.h is at the top of our .h's for each file.
Use #ifdef rather than #if, since these are just defined/not flags.
Use #ifdef rather than #if in this one place; other checks all seem to
be fine.
Pull in generated config file.
Yank all these added -D's on the command line; they get pulled from
the generated header file now.
Whoops, the code looks for USEM4, not just M4.
Convert from using piles of -D compiler flags over to using a
generated header file for config params.