Remove redundant extern keywords from function declarations/definitions. (#1495)

Extern keywords on function declarations/definitions provide no additional value since function declarations/definitions default to external linkage in C99, e.g. removing them won't change the semantics of the program.

The extern keywords were essentially a legacy from the early days of the project. This commit cleans this up across the whole codebase in one go to minimize history disruption.

The bulk of the changes in this commit were produced by a custom clang-tidy checker.

Note that variables declarations carrying the extern keyword are untouched by this commit since there the presence of the keyword actually has an impact on the semantics of the program.

JerryScript-DCO-1.0-Signed-off-by: Tilmann Scheller t.scheller@samsung.com

jerry-core/ecma/builtin-objects/ecma-builtins.h

@@ -65,26 +65,26 @@ typedef enum
 #define ECMA_ACCESSOR_READ_WRITE_GET_GETTER_ID(value) ((uint16_t) ((value) >> 8))
 
 /* ecma-builtins.c */
-extern void ecma_finalize_builtins (void);
+void ecma_finalize_builtins (void);
 
-extern ecma_value_t
+ecma_value_t
 ecma_builtin_dispatch_call (ecma_object_t *, ecma_value_t,
                             const ecma_value_t *, ecma_length_t);
-extern ecma_value_t
+ecma_value_t
 ecma_builtin_dispatch_construct (ecma_object_t *,
                                  const ecma_value_t *, ecma_length_t);
-extern ecma_property_t *
+ecma_property_t *
 ecma_builtin_try_to_instantiate_property (ecma_object_t *, ecma_string_t *);
-extern void
+void
 ecma_builtin_list_lazy_property_names (ecma_object_t *,
                                        bool,
                                        ecma_collection_header_t *,
                                        ecma_collection_header_t *);
-extern bool
+bool
 ecma_builtin_is (ecma_object_t *, ecma_builtin_id_t);
-extern ecma_object_t *
+ecma_object_t *
 ecma_builtin_get (ecma_builtin_id_t);
-extern bool
+bool
 ecma_builtin_function_is_routine (ecma_object_t *);
 
 #endif /* !ECMA_BUILTINS_H */