scons: Prefer winflexbison, and use --wincompat when available.

This avoids MSVC the warning

  warning C4013: 'isatty' undefined; assuming extern returning int

with certain versions of flex.

Reviewed-by: Brian Paul <brianp@vmware.com>

v2: Add win flex-bison link to docs/install.html.
diff --git a/docs/install.html b/docs/install.html
index 9dbfce5..a90c2b2 100644
--- a/docs/install.html
+++ b/docs/install.html
@@ -55,8 +55,8 @@
 <br>
 On Windows with MinGW, install flex and bison with:
 <pre>mingw-get install msys-flex msys-bison</pre>
-For MSVC on Windows, you can find flex/bison programs on the
-<a href="ftp://ftp.freedesktop.org/pub/mesa/windows-utils/">Mesa ftp site</a>.
+For MSVC on Windows, install
+<a href="http://winflexbison.sourceforge.net/">Win flex-bison</a>.
 </li>
 </ul>