intel/compiler: add and fix up fallthrough comments for gcc warnings

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/5714>
diff --git a/src/intel/compiler/brw_compile_sf.c b/src/intel/compiler/brw_compile_sf.c
index 51eb9b0..b750d27 100644
--- a/src/intel/compiler/brw_compile_sf.c
+++ b/src/intel/compiler/brw_compile_sf.c
@@ -167,9 +167,9 @@
    brw_IF(p, BRW_EXECUTE_4);
    {
       switch (c->nr_verts) {
-      case 3: copy_bfc(c, c->vert[2]);
-      case 2: copy_bfc(c, c->vert[1]);
-      case 1: copy_bfc(c, c->vert[0]);
+      case 3: copy_bfc(c, c->vert[2]); /* fallthrough */
+      case 2: copy_bfc(c, c->vert[1]); /* fallthrough */
+      case 1: copy_bfc(c, c->vert[0]); /* fallthrough */
       }
    }
    brw_ENDIF(p);
diff --git a/src/intel/compiler/brw_disasm.c b/src/intel/compiler/brw_disasm.c
index 486f55d..23c55fb 100644
--- a/src/intel/compiler/brw_disasm.c
+++ b/src/intel/compiler/brw_disasm.c
@@ -2064,8 +2064,8 @@
                format(file, ")");
                break;
             }
-            /* FALLTHROUGH */
          }
+         /* FALLTHROUGH */
 
          case GEN7_SFID_PIXEL_INTERPOLATOR:
             if (devinfo->gen >= 7) {