[PATCH] fix format issues in zstd code on 32 bit

Warnings/errors when building 0.3.1.7 on 32 bit, introduced in 380736d0 (tor-0.3.1.1-alpha)

[  103s] src/common/compress_zstd.c: In function 'tor_zstd_get_version_str':
[  103s] src/common/compress_zstd.c:65:19: error: format '%lu' expects argument of type 'long unsigned int', but argument 4 has type 'size_t {aka unsigned int}' [-Werror=format=]
[  103s]                 "%lu.%lu.%lu",
[  103s]                  ~~^
[  103s]                  %u
[  103s]                 version_number / 10000 % 100,
[  103s]                 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
[  103s] src/common/compress_zstd.c:65:23: error: format '%lu' expects argument of type 'long unsigned int', but argument 5 has type 'size_t {aka unsigned int}' [-Werror=format=]
[  103s]                 "%lu.%lu.%lu",
[  103s]                      ~~^
[  103s]                      %u
[  103s] src/common/compress_zstd.c:67:16:
[  103s]                 version_number / 100 % 100,
[  103s]                 ~~~~~~~~~~~~~~~~~~~~~~~~~~
[  103s] src/common/compress_zstd.c:65:27: error: format '%lu' expects argument of type 'long unsigned int', but argument 6 has type 'size_t {aka unsigned int}' [-Werror=format=]
[  103s]                 "%lu.%lu.%lu",
[  103s]                          ~~^
[  103s]                          %u
[  103s] src/common/compress_zstd.c:68:16:
[  103s]                 version_number % 100);
[  103s]                 ~~~~~~~~~~~~~~~~~~~~`

%zu should be used here.

Tested on i586, x86_64, ppc, ppc64, aarch64, armv7. All on GNU gcc 7.2.1 on openSUSE.

Trac:
Username: andreasstieger