support __alignof__ expressions like sizeof()

src/parser/parser.l

@@ -121,6 +121,7 @@ break               return BREAK;
 continue            return CONTINUE;
 
 sizeof              return SIZEOF;
+__alignof__         return ALIGNOF;
 
 __attribute__       return ATTRIBUTE;
 __restrict          return RESTRICT;

src/parser/parser.yc

@@ -103,7 +103,7 @@ int yylex(YYSTYPE *, YYLTYPE *);
 %token CONTINUE;
 
 %token SIZEOF;
-
+%token ALIGNOF;
 
 %token CHAR_CONST;
 %token INT_CONST;
@@ -162,6 +162,8 @@ unary_expression
     | unary_operator cast_expression
     | SIZEOF unary_expression
     | SIZEOF LPAREN type_name RPAREN
+    | ALIGNOF unary_expression
+    | ALIGNOF LPAREN type_name RPAREN
     ;
 
 unary_operator