It fixes an error that happens during building on Alpine Linux:
```
In file included from /tmp/td/tdutils/td/utils/port/path.cpp:7:0:
/tmp/td/tdutils/td/utils/port/path.h: In function 'td::Status td::walk_path(td::CSlice, Func&&)':
/tmp/td/tdutils/td/utils/port/path.h:167:21: error: 'PATH_MAX' was not declared in this scope
curr_path.reserve(PATH_MAX + 10);
^~~~~~~~
```
