meson: define empty variables for libswdri and libswkmsdri

This allows these variables to unconditionally included in `link_with`
lists, even if they're not used. This allows deleting duplicated logic
in nearly every gallium target implemented in meson today. This also
removes the now useless `build_by_default` flag from swdri and swkmsdri.

v4: - add this patch

Fixes: 66c94b9313
       ("meson: build gallium winsys for dri, null, and wrapper")
Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
Acked-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>

src/gallium/meson.build

@@ -29,8 +29,16 @@ subdir('drivers/noop')
 subdir('drivers/trace')
 subdir('drivers/rbug')
 subdir('winsys/sw/null')
-subdir('winsys/sw/dri')
-subdir('winsys/sw/kms-dri')
+if with_dri
+  subdir('winsys/sw/dri')
+else
+  libswdri = []
+endif
+if with_gallium_drisw_kms
+  subdir('winsys/sw/kms-dri')
+else
+  libswkmsdri = []
+endif
 subdir('winsys/sw/wrapper')
 if with_gallium_swr
   if meson.version().version_compare('< 0.44.0')

src/gallium/winsys/sw/dri/meson.build

@@ -1,4 +1,5 @@
 # Copyright © 2017 Dylan Baker
+# Copyright © 2018 Intel Corporation
 
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
@@ -23,5 +24,4 @@ libswdri = static_library(
   files('dri_sw_winsys.c', 'dri_sw_winsys.h'),
   c_args : c_vis_args,
   include_directories : [inc_gallium, inc_include, inc_src, inc_gallium_aux],
-  build_by_default : false,
 )

src/gallium/winsys/sw/kms-dri/meson.build

@@ -1,4 +1,4 @@
-# Copyright © 2017 Intel Corporation
+# Copyright © 2017-2018 Intel Corporation
 
 # Permission is hereby granted, free of charge, to any person obtaining a copy
 # of this software and associated documentation files (the "Software"), to deal
@@ -25,5 +25,4 @@ libswkmsdri = static_library(
   c_args : c_vis_args,
   include_directories : [inc_gallium, inc_include, inc_src, inc_gallium_aux],
   dependencies : dep_libdrm,
-  build_by_default : false,
 )