[sldev] Better build instructions

[Celierra Darling]

Bumping this thread back up...

It looks like Sardonyx Linden started to convert
https://wiki.secondlife.com/wiki/Compiling_the_viewer_(MSVS2005) to
post-cmake instructions, but people haven't realized what had happened
(someone even added "instructions for after 1.21 are not available" a
month later).  So that page was a rather incoherent jumble of both.
This seems to have been confusing a lot of people.

I've temporarily undone Sardonyx's changes, sending people with 1.21+
sources to the cmake page.  But there needs to be some more lasting
solution.  I don't think we ever concluded how exactly to structure
these pages - was there a decision?

Cel