Fix compilation for PS4 libraries

This is a simple compatibility fix for PS4 standard libraries. They don't have Dinkumware-like fpos_t implementation. The minimal code to reproduce problem/check solution:

#include <boost/iostreams/categories.hpp>
#include <boost/iostreams/operations.hpp>

class SourceMock
{
public:
    using char_type = char;
    using category = boost::iostreams::source_tag;
    std::streamsize read(char* /*buffer*/, std::streamsize /*size*/) { return 0; }
};

void foo()
{
    SourceMock source;
    char buffer[42];
    boost::iostreams::read(source, buffer, sizeof(buffer));
}

Output without fix looks like:

1>In file included from foo.ccp:2:
1>In file included from C:\.conan\7fa4fb\1\include\boost/iostreams/operations.hpp:16:
1>In file included from C:\.conan\7fa4fb\1\include\boost/iostreams/close.hpp:19:
1>In file included from C:\.conan\7fa4fb\1\include\boost/iostreams/detail/adapter/non_blocking_adapter.hpp:13:
1>In file included from C:\.conan\7fa4fb\1\include\boost/iostreams/seek.hpp:23:
1>C:\.conan\7fa4fb\1\include\boost/iostreams/positioning.hpp(52,10): error : no matching constructor for initialization of 'std::streampos' (aka 'fpos<_Mbstatet>')
1>C:\Program Files (x86)\SCE\ORBIS SDKs\7.000\target\include\iosfwd(48,2): note: candidate constructor not viable: no known conversion from 'boost::iostreams::stream_offset' (aka 'long') to 'fpos_t' for 2nd argument
1>C:\Program Files (x86)\SCE\ORBIS SDKs\7.000\target\include\iosfwd(43,2): note: candidate constructor not viable: allows at most single argument '_Off', but 2 arguments were provided
1>C:\Program Files (x86)\SCE\ORBIS SDKs\7.000\target\include\iosfwd(38,8): note: candidate constructor (the implicit copy constructor) not viable: requires 1 argument, but 2 were provided
1>C:\Program Files (x86)\SCE\ORBIS SDKs\7.000\target\include\iosfwd(38,8): note: candidate constructor (the implicit move constructor) not viable: requires 1 argument, but 2 were provided

boostorg / iostreams

Fix compilation for PS4 libraries #129

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