build: Enable Vulkan by default

It's still possible to disable via -Dvulkan=disabled

We force-disable it on Mac OS.

I don't know how to best handle it on Windows. Technically we don't need
it, because the Vulkan stuff we want is about dmabufs, but I have no
idea how to convince the build system to toggle the default to
"disabled" on Windows, so it has to stay enabled for now.

.gitlab-ci/test-msvc.bat

@@ -6,7 +6,7 @@ call "C:\Program Files (x86)\Microsoft Visual Studio\2017\BuildTools\VC\Auxiliar
 
 :: FIXME: make warnings fatal
 pip3 install --upgrade --user meson~=0.64 || goto :error
-meson setup -Dbackend_max_links=1 -Ddebug=false -Dmedia-gstreamer=disabled _build || goto :error
+meson setup -Dbackend_max_links=1 -Ddebug=false -Dmedia-gstreamer=disabled -Dvulkan=disabled _build || goto :error
 ninja -C _build || goto :error
 
 goto :EOF

meson.build

@@ -101,6 +101,7 @@ wayland_enabled  = get_option('wayland-backend')
 broadway_enabled = get_option('broadway-backend')
 macos_enabled    = get_option('macos-backend')
 win32_enabled    = get_option('win32-backend')
+vulkan_enabled   = get_option('vulkan')
 
 os_unix   = false
 os_linux  = false
@@ -122,6 +123,7 @@ os_unix = not os_win32
 
 if os_darwin
   wayland_enabled = false
+  vulkan_enabled = false
 else
   macos_enabled = false
 endif
@@ -616,8 +618,8 @@ endif
 # be reported upstream and fixed.
 vulkan_dep = dependency('vulkan',
                         version: vulkan_req,
-                        required: get_option('vulkan'))
-glslc = find_program('glslc', required: get_option('vulkan'))
+                        required: vulkan_enabled)
+glslc = find_program('glslc', required: vulkan_enabled)
 if vulkan_dep.found()
   have_vulkan = true
   vulkan_pkg_found = vulkan_dep.type_name() == 'pkgconfig'

meson_options.txt

@@ -55,8 +55,8 @@ option('print-cups',
 
 option('vulkan',
        type: 'feature',
-       value: 'disabled',
-       description : 'Enable support for the experimental Vulkan renderer')
+       value: 'enabled',
+       description : 'Enable Vulkan support including the Vulkan renderer')
 
 option('cloudproviders',
        type: 'feature',