Check for ucontext.h and sys/ucontext.h

[Joseph S. Myers]

On Sun, 4 Nov 2001, Geoff Keating wrote:

> >  With some more complexity, it should be possible to test
> > for limited target library properties as well, before building libgcc -
> > and so eliminate TARGET_MEM_FUNCTIONS by testing for the ISO C string
> > functions in libc and putting them in libgcc if they aren't in libc.
> 
> One major difficulty there is that glibc requires libgcc to be built
> first.

Glibc wants to link against libgcc, libgcc wants to link against libc.
The bootstrap procedures (for crossing into a new glibc-based target) are
inadequately documented - but it would seem reasonable for the default to
be TARGET_MEM_FUNCTIONS, except when there is a working (linkable against)
libc that does not include the ISO C functions.  (All the platforms in
question are old ones, so presumably not ones where the system libc
depends on libgcc.)

-- 
Joseph S. Myers
jsm28@cam.ac.uk