fix MSYS/MinGW build

MinGW defines __STRICT_ANSI__ when -std=c++0x is specified, which we
have to override in order to get e.g. strdup.  Also, we need to
specify -D_WIN32_WINNT=0x0500 to get post-Windows-2000 functions like
GetModuleHandleEx.  Finally, it seems that GCC 4.8.1 wants us to use
%I64d instead of %lld on Windows.