Fix murmurhash for big-endian architectures.

The murmurhash implementation tries to read a sequence of four bytes as
a single little-endian uint32 value. This does not work on e.g. Linux/s390x;
https://buildd.debian.org/status/fetch.php?pkg=kakoune&arch=s390x&ver=2021.11.08-1&stamp=1645975425&raw=0

src/hash.cc

@@ -41,7 +41,11 @@ size_t hash_data(const char* input, size_t len)
     for (ptrdiff_t i = -nblocks; i; ++i)
     {
         uint32_t key;
+#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
         memcpy(&key, blocks + 4*i, 4);
+#else
+        key = blocks[4*i] + (blocks[4*i + 1] << 8) + (blocks[4*i + 2] << 16) + (blocks[4*i + 3] << 24);
+#endif
         key *= c1;
         key = rotl(key, 15);
         key *= c2;