mesa: Include unistd.h in program_lexer

Which was previously provided implicitly by mtypes.h

CC: Marek Olšák <marek.olsak@amd.com>
CC: Mark Janes <mark.a.janes@intel.com>
Fixes: 43d66c8c2d
       ("mesa: include mtypes.h less")
Signed-off-by: Dylan Baker <dylan.c.baker@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>

src/mesa/program/program_lexer.l

@@ -21,6 +21,7 @@
  * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  * DEALINGS IN THE SOFTWARE.
  */
+#include <unistd.h>
 #include "main/glheader.h"
 #include "main/imports.h"
 #include "program/prog_instruction.h"