Improve crc32 test data

Previously, the buffer used to check that long CRC32 produce the right
results, was initialized with the same value repeated in every byte.
This is subobtimal as it can't detect bugs in which a 8-byte SIMD unit
of data is loaded and processed in the wrong endianness.

Improve the test by initializing the buffer with a pattern that does not
repeat along power-of-two boundaries. 251 was picked as the highest
prime number that fits in a byte.

Author: neuschaefer

unittest/mysys/crc32-t.c

@@ -136,7 +136,8 @@ int main(int argc __attribute__((unused)),char *argv[])
   DO_TEST_CRC32C(0,STR,(sizeof(STR)-1));
   ok(0 == my_crc32c(0, NULL, 0), "crc32c data = NULL, length = 0");
 
-  memset(buf, 0x5a, sizeof buf);
+  for (size_t i = 0; i < sizeof buf; i++)
+    buf[i] = i % 251;
   ok(0 == test_buf(my_checksum, crc32), "crc32 with various lengths");
   ok(0 == test_buf(my_crc32c, crc32c), "crc32c with various lengths");