libs3 ftbfs on ppc64el with -O3

src/util.c:367:13: error: ‘SHA1_transform’ reading 64 bytes from a region of size 63 [-Werror=stringop-overread]
  367 | SHA1_transform(context->state, &(data[i]));
      | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
src/util.c:367:13: note: referencing argument 2 of type ‘const unsigned char[64]’
src/util.c: In function ‘HMAC_SHA1’:
src/util.c:276:13: note: in a call to function ‘SHA1_transform’
  276 | static void SHA1_transform(uint32_t state[5], const unsigned char buffer[64])
      | ^~~~~~~~~~~~~~
cc1: all warnings being treated as errors

-O3 triggers a -Werror=stringop-overread warning. But building the package with -O2 is just fine.