libstdc++/6827: Unreasonable dependencies on ctype.h

[Tony Bryant]

> Synopsis: Unreasonable dependencies on ctype.h
>
<snip>

> State-Changed-Why:
>     I think you are mistaken. The ctype implementation is pretty flexible,
> although a bit baroque.
>
>     See config/os/newlib/bits/ctype* for the default cross compiler bits
> (using newlib.) There is another configuration for glibc (under
> gnu-linux/bits/ctype*). There are also specific configs for most other
> commercial unices. You might check it out.

Firstly, please accept my apologies for presenting this bug report without 
doing enough background research.

Now, I think I've got to the bottom of it, and it appears what is happening 
is configure is setup to pick the newlib "os" interface for most embedded 
cross targets,whereas I'd imagined it would be using the generic "os" 
interface.

If anyone else who is in the same boat as me, the line to change is:

      os_include_dir="config/os/newlib"

in libstdc++-v3/configure.in ; change it to

      os_include_dir="config/os/generic"

and libstdc++ will be built only using the isXXXXX & toXXXXX of the installed 
target ctype.h.

Or just use newlib.

How valid is the assumption that we'll be using always be using newlib on 
cross compilers? 

Is is reasonable for configure to check if newlib is installed, and if 
not, resort to the generic interface?