turnip: guard -Dvulkan-driver=freedreno

Require -DI-love-half-baked-turnips=true as well to enable freedreno
vulkan driver.

meson.build

@@ -206,6 +206,10 @@ with_amd_vk = _vulkan_drivers.contains('amd')
 with_freedreno_vk = _vulkan_drivers.contains('freedreno')
 with_any_vk = _vulkan_drivers.length() != 0 and _vulkan_drivers != ['']
 
+if with_freedreno_vk and get_option('I-love-half-baked-turnips') != true
+  error('Cannot enable freedreno vulkan driver')
+endif
+
 if with_dri_swrast and (with_gallium_softpipe or with_gallium_swr)
   error('Only one swrast provider can be built')
 endif

meson_options.txt

@@ -330,3 +330,9 @@ option(
   value : true,
   description : 'Enable direct rendering in GLX and EGL for DRI',
 )
+option(
+  'I-love-half-baked-turnips',
+  type : 'boolean',
+  value : false,
+  description : 'Allow work-in-progress freedreno vulkan driver to be enabled',
+)