meson: recognize "sunos" as the system name for Solaris

Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Acked-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
diff --git a/meson.build b/meson.build
index e1ca955..e65dcf4 100644
--- a/meson.build
+++ b/meson.build
@@ -124,7 +124,7 @@
 # Only build shared_glapi if at least one OpenGL API is enabled
 with_shared_glapi = with_shared_glapi and with_any_opengl
 
-system_has_kms_drm = ['openbsd', 'netbsd', 'freebsd', 'gnu/kfreebsd', 'dragonfly', 'linux'].contains(host_machine.system())
+system_has_kms_drm = ['openbsd', 'netbsd', 'freebsd', 'gnu/kfreebsd', 'dragonfly', 'linux', 'sunos'].contains(host_machine.system())
 
 dri_drivers = get_option('dri-drivers')
 if dri_drivers.contains('auto')
@@ -885,6 +885,8 @@
 # TODO: this is very incomplete
 if ['linux', 'cygwin', 'gnu', 'gnu/kfreebsd'].contains(host_machine.system())
   pre_args += '-D_GNU_SOURCE'
+elif host_machine.system() == 'sunos'
+  pre_args += '-D__EXTENSIONS__'
 elif host_machine.system() == 'windows'
   pre_args += [
     '-D_WINDOWS', '-D_WIN32_WINNT=0x0601', '-D_WINVER=0x0601',