AM_C*FLAGS and C*FLAGS

[Harlan Stenn]

We are told that we should not use CPPFLAGS or CFLAGS in a Makefile.am,
as they are for users.

The trick is that if we use a configure.ac file to help decide what
flags may be needed, >inside< this configure script we need to use
CFLAGS and CPPFLAGS to effect the running of configure.  (I say CFLAGS
adn CPPFLAGS, but I have a possibly incorrect memory that for configure
tests, they all need to be in CFLAGS.)

Assuming this is true (ie, I am not mistaken), how can one make these
"choices" in a configure script and then "decompose" these choices so
that:

- the right values end up in AM_CFLAGS and AM_CPPFLAGS
- CFLAGS and CPPFLAGS are empty in config.status

H