Add a fully implementation of endian.h

[thisisaname1928]

Add a fully implementation of endian.h

Overview

• Specs: https://pubs.opengroup.org/onlinepubs/9799919799.2024edition/basedefs/endian.h.html, implement all functions, macros listed in the specs.

Functions & Macros

#define LITTLE_ENDIAN
#define BIG_ENDIAN 
#define __LIBC_BYTE_ORDER 

uint16_t  be16toh(uint16_t);
uint32_t  be32toh(uint32_t);
uint64_t  be64toh(uint64_t);
uint16_t  htobe16(uint16_t);
uint32_t  htobe32(uint32_t);
uint64_t  htobe64(uint64_t);
uint16_t  htole16(uint16_t);
uint32_t  htole32(uint32_t);
uint64_t  htole64(uint64_t);
uint16_t  le16toh(uint16_t);
uint32_t  le32toh(uint32_t);
uint64_t  le64toh(uint64_t);