scons: add 'targets' variable, for specifying ... targets

Ideally scons should be able to work backwards from the list of
targets to figure out which drivers, state trackers and other
convenience libraries need to be built.

SConstruct

@@ -31,6 +31,7 @@ import common
 # Configuration options
 
 default_statetrackers = 'mesa'
+default_targets = 'none'
 
 if common.default_platform in ('linux', 'freebsd', 'darwin'):
 	default_drivers = 'softpipe,failover,svga,i915,i965,trace,identity,llvmpipe'
@@ -54,6 +55,28 @@ opts.Add(ListVariable('drivers', 'pipe drivers to build', default_drivers,
 opts.Add(ListVariable('winsys', 'winsys drivers to build', default_winsys,
                      ['xlib', 'vmware', 'i915', 'i965', 'gdi', 'radeon', 'graw-xlib']))
 
+opts.Add(ListVariable('targets', 'driver targets to build', default_targets,
+		      ['dri-i915',
+		       'dri-i965',
+		       'dri-nouveau',
+		       'dri-radeong',
+		       'dri-swrast',
+		       'dri-vmwgfx',
+		       'egl-i915',
+		       'egl-i965',
+		       'egl-nouveau',
+		       'egl-radeon',
+		       'egl-swrast',
+		       'egl-vmwgfx',
+		       'graw-xlib',
+		       'libgl-gdi',
+		       'libgl-xlib',
+		       'xorg-i915',
+		       'xorg-i965',
+		       'xorg-nouveau',
+		       'xorg-radeon',
+		       'xorg-vmwgfx']))
+
 opts.Add(EnumVariable('MSVS_VERSION', 'MS Visual C++ version', None, allowed_values=('7.1', '8.0', '9.0')))
 
 env = Environment(

src/gallium/targets/SConscript

@@ -1,5 +1,8 @@
+import os
 Import('*')
 	
+# Compatibility with old build scripts:
+#
 if 'xlib' in env['winsys']:
 	SConscript([
 		'libgl-xlib/SConscript',
@@ -10,12 +13,7 @@ if 'gdi' in env['winsys']:
 		'libgl-gdi/SConscript',
 	])
 
-if env['platform'] == 'linux' and 'xlib' in env['winsys'] and 'graw-xlib' in env['winsys']:
-	SConscript([
-		'graw-xlib/SConscript',
-	])
-else:
-    if not env['msvc']:
+if not 'graw-xlib' in env['targets'] and not env['msvc']:
         # XXX: disable until MSVC can link correctly
         SConscript('graw-null/SConscript')
 
@@ -30,3 +28,13 @@ if 'xorg' in env['statetrackers']:
 		SConscript([
 			'xorg-vmwgfx/SConscript',
 		])
+
+# Ideally all non-target directories would produce convenience
+# libraries, and the actual shared libraries and other installables
+# would be finally assembled in the targets subtree:
+#
+for target in env['targets']:
+    SConscript(os.path.join(target, 'SConscript'))
+
+
+