HaikuDepot: Improve filter view layout

 * Wrap the two menu fields into a group with unlimited size and give that
   a weight to achieve a stable width for the two which is independent from
   the active menu field entries.
build: Only build WebPositive on x86, x86_gcc2

* Should fix the non-x86 builds
HaikuDepot: Detect more ways to start bullet list items

 * Besides the previous " * ", detect " - ", "* " and "- ".
HaikuDepot: Try slightly harder to keep paragraphs together

 * Some commented-out code to require two line-breaks to start a new
   paragraph. Doesn't work well with current set of packages.
 * If the character before a line-break is a space, do not start a new
   paragraph. Doesn't seem to occur in current package descriptions.
HaikuDepot: Fix invalidating view contents...

... when InvalidateLayout() does not result in a change of the layout.
HaikuDepot: Stableize layout of "About" page contents

 * Give the left group infinite width and use weighting to make it independent
   of the web and email links width.