Remove CFLAGS and external deps from krb5-config --libs

Remove CFLAGS and external deps from krb5-config --libs

r15217 apparently intended to prune $(CFLAGS) from the --libs output,
but actually substituted in the value from the invoker's environment.
Actually prune it.

Don't output external dependencies like -lresolv or -ldl in
krb5-config --libs.  We already don't generate output suitable for
static linking because we omit -lkrb5support, and there is no
expectation that bringing in the krb5 API also brings in the resolv or
dl APIs for the application.

We still output internal dependencies and a com_err dependency; for
instance, e.g. krb5-config --libs gssapi outputs a dependency on -lkrb5
and -lk5crypto, which is inappropriate for a program using only GSSAPI
interfaces.  Removing internal dependencies would likely break callers
who have come to depend on them, especially as we've never correctly
supported things like "krb5-config --libs gssapi krb5" for a program
using multiple APIs.

From stephane@archlinux.org with changes.

ticket: 6965

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@25236 dc483132-0cff-0310-8789-dd5450dbe970