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/base/ecma-literal-storage.h

@@ -36,19 +36,19 @@ typedef struct
   jmem_cpointer_t literal_offset; /**< literal offset */
 } lit_mem_to_snapshot_id_map_entry_t;
 
-extern void ecma_finalize_lit_storage (void);
+void ecma_finalize_lit_storage (void);
 
-extern jmem_cpointer_t ecma_find_or_create_literal_string (const lit_utf8_byte_t *, lit_utf8_size_t);
-extern jmem_cpointer_t ecma_find_or_create_literal_number (ecma_number_t);
+jmem_cpointer_t ecma_find_or_create_literal_string (const lit_utf8_byte_t *, lit_utf8_size_t);
+jmem_cpointer_t ecma_find_or_create_literal_number (ecma_number_t);
 
 #ifdef JERRY_ENABLE_SNAPSHOT_SAVE
-extern bool
+bool
 ecma_save_literals_for_snapshot (uint8_t *, size_t, size_t *,
                                  lit_mem_to_snapshot_id_map_entry_t **, uint32_t *, uint32_t *);
 #endif /* JERRY_ENABLE_SNAPSHOT_SAVE */
 
 #ifdef JERRY_ENABLE_SNAPSHOT_EXEC
-extern bool
+bool
 ecma_load_literals_from_snapshot (const uint8_t *, uint32_t,
                                   lit_mem_to_snapshot_id_map_entry_t **, uint32_t *);
 #endif /* JERRY_ENABLE_SNAPSHOT_EXEC */