macros in .md files

[Joe Buck]

> > The facility already exists for a target to have its MD file passed
> > through CPP.    See md_cppflags in configure.in.
> ...
> First, can we assume that cpp is available without restricting portability?

configure knows how to find the preprocessor and figure out how to invoke
it (in many cases it will do so by invoking the compiler, which must
exist, with special flags).

> Second, won't cpp's concept of C preprocessor tokens cause trouble when
> applied to the md language?

This, I suspect, is the killer.  I'm sure that the feature dates from the
K&R days when the preprocessor had no concept of tokens.  We can't
portably assume that we have a preprocessor that can be made to run in
"traditional" mode.