Reworking the MSVC-related build options

[Norbert Thiebaud]

On Wed, Dec 5, 2012 at 9:43 AM, Tor Lillqvist <tml at iki.fi> wrote:
>> to be able to reproduce a scenario: build using the same config than
>> the one that broke ?
>
> Hmm, but there are tons of stuff that can break in various ways,
> should we have options permanently in there to intentionally reproduce
> all of them?

if something _is_ optional then both way should 'work' (that is not
abend/cpu-loop/eat-you-document if one try to use a feature that
require that 'option' for instance'
And therefore it is usefull to be able to force that options on build.

I'm agreeing completely with you that in the absence of any user
input, autogen should pick up the mos recent VS available and DirectX
if available etc..
I also strongly agree that a single argument to select the VS version
when one has more than one is desirable to select a
consistent/coherent set of values
but still the ability to override is still desirable in corner case...
that may not have to be via argument from the command line.. that can
also
be like for CC, if the value is set in the env, then honor it,
otherwise find a best effort value.

Norbert

PS: if there are combination of options that are not supported,
autogen _should_ ideally block them. for instance if system-python is
incompatible with internal-openssl, then that should be detected and
blocked at configure time.