Unusual CPP idiom used in some libio files

[rodneybrown@pmsc.com]

Some of the libio files use an unusual, though ANSI, CPP idiom,
should they?

egcs-19981012/libio/iostream.cc:#if defined __GLIBC__ && __GLIBC__ >= 2
egcs-19981012/libio/iostream.cc:#elif defined  _IO_USE_DTOA
egcs-19981012/libio/iostream.cc:#if defined __GLIBC__ && __GLIBC__ >= 2
egcs-19981012/libio/libio.h:# if defined __GNUG__ && \
egcs-19981012/libio/libio.h:# if defined __GLIBC__ && __GLIBC__ >= 2
egcs-19981012/libio/libioP.h:#if defined __GLIBC__ && __GLIBC__ >= 2
egcs-19981012/libio/libioP.h:# if defined __GNUG__ && \