Includes known Valgrind warnings in our dependencies that cannot be
fixed in-tree.

Example use:

$ valgrind --suppressions=contrib/valgrind.supp src/test/test_bitcoin
$ valgrind --suppressions=contrib/valgrind.supp --leak-check=full \
      --show-leak-kinds=all src/test/test_bitcoin --log_level=test_suite

valgrind --suppressions=contrib/valgrind.supp src/test/test_bitcoin

==24741== HEAP SUMMARY:
==24741==     in use at exit: 1,050,552 bytes in 15 blocks
==24741==   total heap usage: 47,594,831 allocs, 47,594,816 frees,
5,662,452,623 bytes allocated
==24741==
==24741== LEAK SUMMARY:
==24741==    definitely lost: 0 bytes in 0 blocks
==24741==    indirectly lost: 0 bytes in 0 blocks
==24741==      possibly lost: 0 bytes in 0 blocks
==24741==    still reachable: 1,049,592 bytes in 11 blocks
==24741==         suppressed: 960 bytes in 4 blocks