Fix builds with recent C compilers

[nabijaczleweli]

nabijaczleweli@tarta:~/work/bsontest$ iex -S mix
Erlang/OTP 25 [erts-13.1.5] [source] [64-bit] [smp:24:24] [ds:24:24:10] [async-threads:1] [jit:ns]

===> Fetching pc v1.15.0
===> Analyzing applications...
===> Compiling pc
===> Compiling /home/nabijaczleweli/work/bsontest/deps/inotify/c_src/erl_comm.c ===> /home/nabijaczleweli/work/bsontest/deps/inotify/c_src/erl_comm.c:49:5: error: call to undeclared library function 'memset' with type 'void *(void *, int, unsigned long)'; ISO C99 and later do not support implicit function declarations [-Wimplicit-function-declaration]
   49 |     memset(*pbuf, 0, len - (*size));
      |     ^
/home/nabijaczleweli/work/bsontest/deps/inotify/c_src/erl_comm.c:49:5: note: include the header <string.h> or explicitly provide a declaration for 'memset'
1 error generated.

** (Mix) Could not compile dependency :inotify, "/home/nabijaczleweli/.mix/elixir/1-17/rebar3 bare compile --paths /home/nabijaczleweli/work/bsontest/_build/dev/lib/*/ebin" command failed. Errors may have been logged above. You can recompile this dependency with "mix deps.compile inotify --force", update it with "mix deps.update inotify" or clean it with "mix deps.clean inotify"