Compiler warnings in Windows (MinGW) build

Target bitshares-core 5.1.0

> -- Using custom FindBoost config
CMake Warning at /usr/share/cmake-3.10/Modules/FindBoost.cmake:801 (message):
New Boost version may have incorrect or missing dependencies and imported
targets
Call Stack (most recent call first):
/usr/share/cmake-3.10/Modules/FindBoost.cmake:907 (_Boost_COMPONENT_DEPENDENCIES)
/usr/share/cmake-3.10/Modules/FindBoost.cmake:1558 (_Boost_MISSING_DEPENDENCIES)
libraries/fc/CMakeModules/Boost/BoostConfig.cmake:6 (find_package)
CMakeLists.txt:200 (FIND_PACKAGE)

> -- Found Doxygen: /usr/bin/doxygen (found version "1.8.13") found components: doxygen missing components: dot

>In file included from /home/ubuntu/build/lib/include/boost/thread/shared_mutex.hpp:22,
from /home/ubuntu/build/lib/include/boost/thread/detail/thread_group.hpp:10,
from /home/ubuntu/build/lib/include/boost/thread/thread.hpp:13,
from /home/ubuntu/build/lib/include/boost/thread.hpp:13,
from /home/ubuntu/build/bitshares/libraries/fc/include/fc/asio.hpp:7,
from /home/ubuntu/build/bitshares/libraries/fc/include/fc/network/tcp_socket.hpp:6,
from /home/ubuntu/build/bitshares/libraries/net/include/graphene/net/message_oriented_connection.hpp:25,
from /home/ubuntu/build/bitshares/libraries/net/message_oriented_connection.cpp:31:
/home/ubuntu/build/lib/include/boost/thread/win32/shared_mutex.hpp: In member function 'boost::shared_mutex::state_data boost::shared_mutex::interlocked_compare_exchange(boost::shared_mutex::state_data*, boost::shared_mutex::state_data, boost::shared_mutex::state_data)':
/home/ubuntu/build/lib/include/boost/thread/win32/shared_mutex.hpp:49:98: warning: dereferencing type-punned pointer will break strict-aliasing rules [-Wstrict-aliasing]
*reinterpret_cast(&new_value),
...

> /home/ubuntu/build/bitshares/libraries/fc/src/string.cpp:162:17: warning: this statement may fall through [-Wimplicit-fallthrough=]
m *= thousand;
(and etc)

> /home/ubuntu/build/bitshares/libraries/fc/include/fc/io/json_relaxed.hpp: In function 'std::__cxx11::string fc::json_relaxed::stringFromStream(T&) [with T = fc::stringstream; bool strict = false]':
/home/ubuntu/build/bitshares/libraries/fc/include/fc/io/json_relaxed.hpp:197:18: warning: this statement may fall through [-Wimplicit-fallthrough=]
if( strict )
^~
/home/ubuntu/build/bitshares/libraries/fc/include/fc/io/json_relaxed.hpp:200:14: note: here
case '"':
^~~~
(and etc)

> /home/ubuntu/build/bitshares/libraries/fc/src/rpc/cli.cpp:229:12: warning: 'fc::rpc::cli_quitting' defined but not used [-Wunused-variable]
static int cli_quitting = false;
^~~~~~~~~~~~
/home/ubuntu/build/bitshares/libraries/fc/src/rpc/cli.cpp:217:12: warning: 'int fc::rpc::cli_check_secret(const char*)' defined but not used [-Wunused-function]
static int cli_check_secret(const char *source)
^~~~~~~~~~~~~~~~
/home/ubuntu/build/bitshares/libraries/fc/src/rpc/cli.cpp:184:12: warning: 'int fc::rpc::cli_completion(char*, char***)' defined but not used [-Wunused-function]
static int cli_completion(char *token, char ***array)
^~~~~~~~~~~~~~
/home/ubuntu/build/bitshares/libraries/fc/src/rpc/cli.cpp:128:14: warning: 'char* fc::rpc::my_rl_complete(char*, int*)' defined but not used [-Wunused-function]
static char *my_rl_complete(char *token, int *match)
^~~~~~~~~~~~~~

> /home/ubuntu/build/bitshares/libraries/fc/src/rpc/state.cpp: In member function 'fc::rpc::request fc::rpc::state::start_remote_call(const string&, fc::variants)':
/home/ubuntu/build/bitshares/libraries/fc/src/rpc/state.cpp:48:62: warning: missing initializer for member 'fc::rpc::request::jsonrpc' [-Wmissing-field-initializers]
request request{ _next_id++, method_name, std::move(args) };

> /home/ubuntu/build/bitshares/libraries/fc/src/rpc/websocket_api.cpp:119:91: warning: missing initializer for member 'fc::rpc::request::jsonrpc' [-Wmissing-field-initializers]
fc::rpc::request req{ optional(), "notice", { callback_id, std::move(args) } };

> /home/ubuntu/build/bitshares/libraries/fc/src/rpc/websocket_api.cpp:138:85: warning: missing initializer for member 'fc::rpc::error_object::data' [-Wmissing-field-initializers]
return response( variant(), { -32600, "Batch requests not supported" }, "2.0" );
(and etc)

> /home/ubuntu/build/bitshares/libraries/fc/src/log/console_appender.cpp:52:29: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
if (my->cfg.stream = stream::std_error)
~~~~~~~~~~~~~~~^~~~~~~~
/home/ubuntu/build/bitshares/libraries/fc/src/log/console_appender.cpp:54:34: warning: suggest parentheses around assignment used as truth value [-Wparentheses]
else if (my->cfg.stream = stream::std_out)

> /home/ubuntu/build/bitshares/libraries/fc/src/crypto/aes.cpp: In destructor 'fc::openssl_thread_config::~openssl_thread_config()':
/home/ubuntu/build/bitshares/libraries/fc/src/crypto/aes.cpp:439:32: warning: the address of 'static long unsigned int fc::openssl_thread_config::get_thread_id()' will never be NULL [-Waddress]
if (CRYPTO_get_id_callback() == &get_thread_id)

Start by reproducing the BitShares 5.1.0 MinGW build and review the warnings from CMakeLists.txt, libraries/fc/src/string.cpp, fc/io/json_relaxed.hpp, and the fc/src/rpc, log, and crypto files listed here. Done means the reported project warnings are addressed or explicitly separated from external Boost and Doxygen warnings, with the build completing cleanly.

Written by the indexing model from the issue text.