add cstddef explicitly for GCC11

[hv15]

On ArchLinux with CUDA 11.4 and GCC11, one gets the following error message when compile xmrig-cuda:

[ 82%] Building CXX object CMakeFiles/xmrig-cuda.dir/src/crypto/common/Algorithm.cpp.o
In file included from /home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.cpp:20:
/home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.h:88:29: error: ‘size_t’ does not name a type
   88 |     static inline constexpr size_t l2(Id id)                { return family(id) == RANDOM_X ? (1U << ((id >> 8) & 0xff)) : 0U; }
      |                             ^~~~~~
In file included from /home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.cpp:20:
/home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.h:25:1: note: ‘size_t’ is defined in header ‘<cstddef>’; did you forget to ‘#include <cstddef>’?
   24 | #include <vector>
  +++ |+#include <cstddef>
   25 | 
In file included from /home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.cpp:20:
/home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.h:89:29: error: ‘size_t’ does not name a type
   89 |     static inline constexpr size_t l3(Id id)                { return 1ULL << ((id >> 16) & 0xff); }
      |                             ^~~~~~
/home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.h:89:29: note: ‘size_t’ is defined in header ‘<cstddef>’; did you forget to ‘#include <cstddef>’?
/home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.h:97:12: error: ‘size_t’ does not name a type
   97 |     inline size_t l2() const                                { return l2(m_id); }
      |            ^~~~~~
/home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.h:97:12: note: ‘size_t’ is defined in header ‘<cstddef>’; did you forget to ‘#include <cstddef>’?
/home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.h:101:12: error: ‘size_t’ does not name a type
  101 |     inline size_t l3() const
      |            ^~~~~~
/home/dragonek/.cache/paru/clone/xmrig-cuda/src/xmrig-cuda-6.15.0/src/crypto/common/Algorithm.h:101:12: note: ‘size_t’ is defined in header ‘<cstddef>’; did you forget to ‘#include <cstddef>’?

Clearly size_t is not defined, and including <cstddef> solves this. I know that with GCC4/5 that cstddef was pulled out of a lot of headers, making it necessary to explicitly include it. Maybe with GCC11 this also happened; the GNU release notes don't list this though.

[ludiazv]

Confirmed. This fixes compilation under GCC11. Please merge!

[GibsDev]

I also had this issue, and this solved it.

[D3PSI]

I have encountered this very same problem and can only second this. This fixes compilation problem for GCC 11.1.0.

[Spudz76]

@xmrig plz merge thx

[AquilaFasciata]

Successfully compiled. Please merge.