Don't weed out wall and floor sprites when spawning Build sprites
Remove slopetype from line_t.

- Recomputing it in the only two places where it's used is trivial, so
  it's basically a waste of space to precompute it.
Remove polymost stuff

- Maybe it will be back someday, but it's been essentially dead for nearly
  10 years, so don't hold your breath.
Consolidate wall texturing vars into two structs

- All transformation and clipping values go into FWallCoords.
- All texture mapping values go into FWallTMapVals.
Pass WallC as a parameter to (O)WallMost instead of referencing it globally
Pass x1 and x2 to Prep(L)Wall as params
Consolidate some common code for texture mapping setup

- R_AddLine() and R_RenderDecal() had nearly identical code for setting up
  texture mapping. These have now been spun off into methods of
  FWallCoords and FWallTmapVals.
Set face/wall/floor flags from Build sprites
Add CVar for drawing weapons in the althud
Fixed build on compilers other than MSVC

No more "Call to 'LittleShort' is ambiguous" error
Merge branch 'fix_build_nonmsvc' of https://github.com/alexey-lysiuk/gzdoom
- added menu entry for newly added hud_showweapons CVAR.
Q&D port of decal code to draw generic wall sprites

- This still doesn't use all the sprite properties correctly. It also
  looks like they're going to need different code to build the clipping
  arrays. But at least wall sprites are drawn at the proper angle now!
Merge branch 'master' of github.com:rheit/zdoom
Merge branch 'master' of https://github.com/rheit/zdoom
- split off sprite clipping adjustment code into its own function.
- implemented rendering of wall sprites.
- fixed incorrect function call in shader compiler.