build: fix char signed vs unsigned warning (#23675)
build: fix char signed vs unsigned warning (#23675)

char defaults to signed on most x86 platforms, but unsigned on arm64.
When targeting linux arm64 this produced a warning because character was
always >= 0. This change circumvents this warning without changing
behavior even though it seems pretty unreasonable to have a character
less than 0 in this use case. Theoretically we could disable a warning
flag instead but that differs between clang and gcc.

Fixes https://github.com/envoyproxy/envoy/issues/23569

Signed-off-by: Keith Smiley <cadcacca0656fa2178c91a0e61e28374cd3a79c3@gmail.com>

Signed-off-by: Keith Smiley <cadcacca0656fa2178c91a0e61e28374cd3a79c3@gmail.com>
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