downgrade POSIX C source version to 2001-12

Implement `strdup` to not require version 2008-09

Makefile

@@ -2,7 +2,7 @@ CC ?= gcc
 DEBUG ?= 0
 
 CFLAGS = -Wall -Werror -Wextra -Wpedantic -std=c99 -Ofast \
--D_POSIX_C_SOURCE=200809L
+-D_POSIX_C_SOURCE=200112L
 
 ifeq ($(DEBUG), 1)
 	CFLAGS += -g -DDEBUG

include/common.h

@@ -6,6 +6,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/types.h>
 
 /* enums */
 enum configurations_bitshift {

include/strdup.h

@@ -0,0 +1,11 @@
+#ifndef _STRDUP_H
+#define _STRDUP_H
+
+#include <errno.h>
+#include <stdlib.h>
+#include <string.h>
+
+/* functions definitions */
+char* strdup(const char* s);
+
+#endif /* _STRDUP_H */

src/main.c

@@ -23,6 +23,7 @@
 #include "atoumax_base10.h"
 #include "corrupter.h"
 #include "file_type.h"
+#include "strdup.h"
 
 /* enums */
 enum arg_destinations {

src/strdup.c

@@ -0,0 +1,17 @@
+#include "strdup.h"
+
+/* function implementations */
+char* strdup(const char* s) {
+	if (s == NULL) {
+		errno = EINVAL;
+		return NULL;
+	}
+
+	char* copy = malloc((strlen(s) + 1) * sizeof(char));
+	if (copy == NULL)
+		return NULL;
+
+	strcpy(copy, s);
+
+	return copy;
+}