Still a few flaws in configure's default CFLAGS selection

While fooling with adding -fno-strict-aliasing to configure, I realized
that there are still some oddities about its selection of CFLAGS. The
problems stem from the fact that autoconf will always select a default
value of CFLAGS that includes "-g", if the compiler accepts "-g" at all.
This has a couple of consequences:

1. --enable-debug is nearly useless, since unless you've manually
specified CFLAGS, what you're going to get will include -g anyway.

2. The code Bruce put in to default to "-O" on non-gcc compilers
will never actually fire.

It would be fairly easy to override autoconf's behavior, but I wonder
whether that will surprise people who are used to the "standard"
behavior of autoconf scripts. Personally I've always felt that
defaulting to -g was a bizarre and unwise choice on the part of the
autoconf developers, but maybe someone out there wants to defend it?

Comments anyone?

regards, tom lane