[6X]: backport of 7x gpcloud commit f14dbd7. gpcloud: use memcpy to avoid -Wstringop-truncation

[reshke]

I have noticed such a warn while compiling gpcloud for 6X_STABLE. Lets fix this the similar way it is done in master 2 years ago. I have simply cherry-picked f14dbd7e9d492ce36f3cf292f6d5c301e9da2ac4

Original commit msg:

Latest version of GCC detects string truncation and gives warnings.
However here is by design, use memcpy instead to avoid the warning.

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