exported in the environment. Without it, merely setting the CFLAGS
environment variable would not affect the compilation of the parser,
though it was still possible to override it by passing the variable
as an argument (e.g. make all CFLAGS="-Oinsane -Wextra-special").

It also makes the default CFLAGS for the parser consistent with
the default for the C++ dfa library, and passes the flags on to
the library.

An audit of the other bits of C showed that they either supported
CFLAGS during configure or were otherwise honoring CFLAGS when set
as environment variable.