-fPIC warning for every file while compiling for Windows #3607

When compiling for windows using gitian, every file gives a (seemingly harmless) warning.

 CXX    libbitcoinqt_a-trafficgraphwidget.o
trafficgraphwidget.cpp:1:0: warning: -fPIC ignored for target (all code is position independent) [enabled by default]
 CXX    libbitcoinqt_a-utilitydialog.o
utilitydialog.cpp:1:0: warning: -fPIC ignored for target (all code is position independent) [enabled by default]
 CXX    libbitcoinqt_a-addressbookpage.o
addressbookpage.cpp:1:0: warning: -fPIC ignored for target (all code is position independent) [enabled by default]

More warnings that only appear during the windows build (both 32 and 64 bit). Probably harmless, but I'm not sure:

/home/ubuntu/staging32/include/boost/interprocess/detail/win32_api.hpp:903:116: warning: declaration of ‘void* boost::interprocess::winapi::CreateMutexA(boost::interprocess::winapi::interprocess_security_attributes*, int, const char*)’ with C language linkage [enabled by default]
/home/ubuntu/staging32/include/boost/thread/win32/thread_primitives.hpp:144:55: warning: conflicts with previous declaration ‘void* boost::detail::win32::CreateMutexA(boost::detail::win32::_SECURITY_ATTRIBUTES*, int, const char*)’ [enabled by default]
/home/ubuntu/staging32/include/boost/interprocess/detail/win32_api.hpp:908:127: warning: declaration of ‘void* boost::interprocess::winapi::CreateSemaphoreA(boost::interprocess::winapi::interprocess_security_attributes*, long int, long int, const char*)’ with C language linkage [enabled by default]
/home/ubuntu/staging32/include/boost/thread/win32/thread_primitives.hpp:145:55: warning: conflicts with previous declaration ‘void* boost::detail::win32::CreateSemaphoreA(boost::detail::win32::_SECURITY_ATTRIBUTES*, long int, long int, const char*)’ [enabled by default]

These only happen while building init.cpp, not for every file.

This would be solved by libtool. Mentioning because it'd come in as part of #3989 if we decide to go that route.