The conversion given assumed two things:
1. the pointer was either 32-bit aligned or that unaligned word access
was safe. (Not the case on ARM)
We avoid this by using memcpy to copy to a buffer that *is*
32-bit-word-aligned.
2. the word was in native-endian format.
The original code appeared to assume the given word would be in
big-endian format (aka "network" byte order), so we convert it to the
host's native format before casting.
We re-instate the original implementation, controlled by a compiler
switch to allow easy rollback if problems are encountered.
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