Fix GCC 8.1 warnings#4646
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Our provided callback function `threadid_cb(CRYPTO_THREADID *threadid)` sets up a unique thread ID by asking pthread for the current thread ID. Since openssl version 1.1, `CRYPTO_THREADID_set_numeric` is simply a no-op macro, leaving the `threadid` argument unused after the preprocessor has processed the macro. GCC does not account for that situation and will thus complain about `threadid` being unused. Silence this warning by using `GIT_UNUSED(threadid)`.
Since version 8.1, GCC will do some automatic bounds checking when printing static content into a buffer with known size. The bounds checking doesn't yet work quite right in all scenarios and may thus lead to false positives. Fix one of these false positives in refs::normalize by simplifying the code.
Since GCC 8.1, the compiler performs some bounds checking when copying static data into arrays with a known size. In one test, we print a format string of "%s/sub%02d" into a buffer of 64 bytes. The input buffer for the first "%s" is bounded to at most 63 characters, plus four bytes for the static string "/sub" plus two more bytes for "%02d". Thus, our target buffer needs to be at least 70 bytes in size, including the NUL byte. There seems to be a bug in the analysis, though, because GCC will not account for the limiting "%02" prefix, treating it as requiring the same count of bytes as a "%d". Thus, we end up at 79 bytes that are required to fix the warning. To make it look nicer and less special, we just round the buffer size up to 80 bytes.
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Fixes required to build with -DENABLE_WERROR=ON and GCC 8.1