Turns out that the precautions against winelib builds failing, which I
put in years ago because I was using winelib as a build setup for
Coverity testing, are all obsolete. My Coverity build scripts runs
fine now without any of them.

It seems to have caused a compile error, apparently due to a mismatch
between compiler predefines (__SSE2__) and header files (emmintrin.h).
The easiest thing is to just turn off the hardware version completely,
so the rest of the code can still be scanned.

In commit 188e2525 I removed it from Winelib builds in general on the
grounds that Winelib had acquired that function. But now that I come
to try a Coverity build, I find that that is still one Winelib build
that does fail if I call SecureZeroMemory.

It's really only useful with MinGW rather than a Cygwin toolchain these
days, as recent versions of the latter insist against linking with the
Cygwin DLL.

(I think it may no longer be possible to build with Cygwin out of the
box at all these days, but I'm not going to say so without having
actually checked that's the case. Settle for listing MinGW first in
various comments and docs.)

I've shifted away from using the SVN revision number as a monotonic
version identifier (replacing it in the Windows version resource with
a count of days since an arbitrary epoch), and I've removed all uses
of SVN keyword expansion (replacing them with version information
written out by Buildscr).

While I'm at it, I've done a major rewrite of the affected code which
centralises all the computation of the assorted version numbers and
strings into Buildscr, so that they're all more or less alongside each
other rather than scattered across multiple source files.

I've also retired the MD5-based manifest file system. A long time ago,
it seemed like a good idea to arrange that binaries of PuTTY would
automatically cease to identify themselves as a particular upstream
version number if any changes were made to the source code, so that if
someone made a local tweak and distributed the result then I wouldn't
get blamed for the results. Since then I've decided the whole idea is
more trouble than it's worth, so now distribution tarballs will have
version information baked in and people can just cope with that.

[originally from svn r10262]

The winegcc hack I use for my Coverity builds is currently using a
version of wincrypt.h that's missing a couple of constants I use.
Ensure they're defined by hand, but (just in case I defined them
_wrong_) also provide a command-line define so I can do that only in
the case of Coverity builds.

[originally from svn r10234]

[originally from svn r9969]