compressed errno strings

[ZERICO2005]

Compressed the errno strings used for strerror/perror. The lookup table is 79 * 3 = 237 bytes smaller, at the cost of 28 bytes of code, yielding a net savings of 209 bytes.

The downside is that retrieving the errno strings is now O(N) instead of O(1). However, the worst case retrieval time is ~0.8 milliseconds. (31ms to effectively do for (int i = 0; i < 79; i++) { strerror(i); })

// 3 bytes of overhead to store pointers to each string
static char const * const errno_strings[] = {
    "no error",
    "EPERM",
    "EINVAL",
    "EIO",
    "EDOM",
    "ERANGE",
    "EILSEQ",
};

// no overhead
static constexpr char errno_strings[] = {
    "no error"
    "\0EPERM"
    "\0EINVAL"
    "\0EIO"
    "\0EDOM"
    "\0ERANGE"
    "\0EILSEQ"
};