[PATCH] PowerPC: define _CALL_ELF if compiler does not define it

[Roland McGrath]

It seems questionable to modify CFLAGS for this.  It probably belongs in
CPPFLAGS, to begin with.  But I'm not sure I like it modifying the user's
CPPFLAGS either.  It might be best to add a new config.make variable for
configure-deduced (as opposed to user-specified) CPPFLAGS and accumulate
into that.  It would be an analogue to config-extra-cflags
(libc_extra_cflags in configure).  While you're at it, generalize
libc_extra_cflags so it accumulates and could be used by sysdeps configure
fragments, rather than just being single-purpose as it is today.