Change configure argument handling to be more in line with standard autoconf

Change configure argument handling to be more in line with standard autoconf
usage.

* aclocal.m4 (KRB5_AC_CHOOSE_ET, KRB5_AC_CHOOSE_SS): Renamed from non-KRB5_AC_
names.  Change --with-system-com_err to --with-system-et, to avoid confusing
mix of '-' and '_'.
(WITH_CCOPTS): Describe as deprecated in favor of CFLAGS=...; use
AC_REQUIRE_CPP.
(WITH_LINKER, WITH_LDOPTS, WITH_CPPOPTS): Describe as deprecated; encourage use
of LD= etc instead.
(WITH_NETLIB, WITH_HESIOD): Use AC_HELP_STRING.
(KRB5_AC_CHECK_FOR_CFLAGS): New macro.
(WITH_CC): Mark old configure option deprecated, encourage user to use CC=
instead.  Add gcc warning flags only if CFLAGS not set by user.  Don't force
default to "cc".
(KRB5_LIB_PARAMS): Use AC_CANONICAL_HOST, don't bother with cache.

git-svn-id: svn://anonsvn.mit.edu/krb5/trunk@14803 dc483132-0cff-0310-8789-dd5450dbe970