gallium: Add warnings incase pipe drivers are not built in targets

src/gallium/targets/dri-i915/SConscript

@@ -1,5 +1,9 @@
 Import('*')
 
+if not 'i915' in env['drivers']:
+    print 'warning: i915 pipe driver not built skipping i915_dri.so'
+    Return()
+
 env = drienv.Clone()
 
 env.ParseConfig('pkg-config --cflags --libs libdrm_intel')

src/gallium/targets/dri-i965/SConscript

@@ -1,5 +1,9 @@
 Import('*')
 
+if not 'i965' in env['drivers']:
+    print 'warning: i965 pipe driver not built skipping i965_dri.so'
+    Return()
+
 env = drienv.Clone()
 
 env.ParseConfig('pkg-config --cflags --libs libdrm_intel')

src/gallium/targets/dri-radeong/SConscript

@@ -1,5 +1,9 @@
 Import('*')
 
+if not 'r300' in env['drivers']:
+    print 'warning: r300 pipe driver not built skipping radeong_dri.so'
+    Return()
+
 env = drienv.Clone()
 
 env.ParseConfig('pkg-config --cflags --libs libdrm_radeon')

src/gallium/targets/dri-vmwgfx/SConscript

@@ -1,5 +1,9 @@
 Import('*')
 
+if not 'svga' in env['drivers']:
+    print 'warning: svga pipe driver not built skipping vmwgfx_dri.so'
+    Return()
+
 env = drienv.Clone()
 
 drivers = [

src/gallium/targets/xorg-vmwgfx/SConscript

@@ -2,6 +2,10 @@ import os.path
 
 Import('*')
 
+if not 'svga' in env['drivers']:
+    print 'warning: svga pipe driver not built skipping vmwgfx_drv.so'
+    Return()
+
 if env['platform'] == 'linux':
 
 	env = env.Clone()