Changeset 04e4829 in rtems for c/src/lib/include/sys

Patch rtems-rc-20000626-1.diff from Ralf Corsepius <corsepiu@…>.
Comments follow:

Building linux/posix fails due to including lib/include/sys/cdefs.h
instead of linux's sys/cdefs.h.
AFAIS, this sys/cdefs.h is specific to newlib and should probably
not be used on any unix host.

Therefore, I changed the relevant Makefile.am/configure.in to
condionally install sys/cdefs.h only if newlib is present.

This triggered another bug inside of the newlib-check for one of
RTEMS target's (Unfortunately I can't remember which - mips/i960 ?
... one of the more exotic ...), for which int func() isn't
identical to void func().

Note: This patch needs to be tested under Cygwin and Solaris. I am
particularily unsure about Cygwin/posix, as it applies a different
version newlib which must not trigger RTEMS newlib check (it is
supposed to fail) and if it may need RTEMS's sys/cdefs.h.