re PR libstdc++/4150 (catastrophic performance decrease in C++ code)

re PR libstdc++/4150 (catastrophic performance decrease in C++ code)

        PR libstdc++/4150
        * include/std/std_streambuf.h (basic_streambuf::_M_set_indeterminate):
        Move to filebuf.
        (basic_streambuf::_M_set_determinate): Likewise.
        (basic_streambuf::_M_is_indeterminate): Likewise.
        * include/bits/std_fstream.h (basic_filebuf::_M_filepos): New
        non-static data member.
        (basic_filebuf::_M_underflow_common): New non-static member function.
        (basic_filebuf::_M_underflow, _M_uflow): Call it.
        (basic_filebuf::sync): Avoid useless seeking.
        (basic_filebuf::_M_set_indeterminate): Move here from streambuf.
        Set _M_filepos.
        (basic_filebuf::_M_set_determinate): Likewise.
        (basic_filebuf::_M_is_indeterminate): Likewise.
        * include/bits/fstream.tcc (basic_filebuf::_M_really_overflow): Seek
        back to _M_out_beg if necessary.
        (basic_filebuf::seekoff): Likewise.
        (basic_filebuf::_M_underflow_common): Generalization of old
        underflow().  Don't seek back to _M_in_beg.
        * src/ios.cc: Lose _GLIBCPP_AVOID_FSEEK stuff.
        * config/os/solaris/solaris2.?/bits/os_defines.h: Likewise.
        * config/os/bsd/freebsd/bits/os_defines.h: Likewise.
        * config/os/mingw32/bits/os_defines.h: Likewise.
        * testsuite/27_io/filebuf_virtuals.cc (test05): Don't overspecify
        ungetc test.

From-SVN: r52634