Add clang::fallthrough annotations to bison templates

Test: build aidl with new templates, no more warning
Change-Id: Id5bd595e3e11f0b414e4475a5ec55113350dbc5a
diff --git a/data/glr.c b/data/glr.c
index 02a76c2..08d4a3e 100644
--- a/data/glr.c
+++ b/data/glr.c
@@ -635,6 +635,9 @@
             if (*++yyp != '\\')
               goto do_not_strip_quotes;
             /* Fall through.  */
+#if defined(__has_cpp_attribute) && __has_cpp_attribute(clang::fallthrough)
+            [[clang::fallthrough]];
+#endif
           default:
             if (yyres)
               yyres[yyn] = *yyp;
diff --git a/data/lalr1.cc b/data/lalr1.cc
index 237b246..c6e1977 100644
--- a/data/lalr1.cc
+++ b/data/lalr1.cc
@@ -376,6 +376,9 @@
               if (*++yyp != '\\')
                 goto do_not_strip_quotes;
               /* Fall through.  */
+#if defined(__has_cpp_attribute) && __has_cpp_attribute(clang::fallthrough)
+              [[clang::fallthrough]];
+#endif
             default:
               yyr += *yyp;
               break;
diff --git a/data/yacc.c b/data/yacc.c
index b34549f..17ad67c 100644
--- a/data/yacc.c
+++ b/data/yacc.c
@@ -1209,6 +1209,9 @@
 	    if (*++yyp != '\\')
 	      goto do_not_strip_quotes;
 	    /* Fall through.  */
+#if defined(__has_cpp_attribute) && __has_cpp_attribute(clang::fallthrough)
+	    [[clang::fallthrough]];
+#endif
 	  default:
 	    if (yyres)
 	      yyres[yyn] = *yyp;