Support __extension__

src/parser/parser.l

@@ -126,6 +126,7 @@ __attribute__       return ATTRIBUTE;
 __restrict          return RESTRICT;
 asm                 return ASM;
 __asm__             return ASM;
+__extension__       return EXTENSION;
 
 L?'[^\\]'           return CHAR_CONST;
 L?'\\.'             return CHAR_CONST;

src/parser/parser.yc

@@ -115,6 +115,7 @@ int yylex(YYSTYPE *, YYLTYPE *);
 %token ATTRIBUTE;
 %token RESTRICT;
 %token ASM;
+%token EXTENSION;
 
 %start translation_unit
 
@@ -424,6 +425,7 @@ type_qualifier
     : CONST
     | VOLATILE
     | RESTRICT
+    | EXTENSION
     ;
 
 declarator