#3 Respect well-known environment variables

[Christian Biere]

It would be nice if Configure respected well-known
environment variables such as CC, CPP, LDFLAGS, CFLAGS,
CPPFLAGS. These are useful to have some sane and
preferred defaults. There are other ways to achieve the
same but those are more of a hassle or rather
intrusive (such as wrappers, aliases, PATH etc.). dist
already has cc, ccflags, ldflags and I don't see why
these can't or shouldn't default to the respective
environment variables iff set. Those who find using
environment variables for such purposes ugly, don't have
to use them. Maybe the dist modules should explicitely
show when they default to variable contents, in case a
user isn't aware that his environment contains a certain
variable which has an effect on Configure.