[Bug target/77894] Enable GNU indirect function support by default as it will be used in glibc.

["nsz at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77894

--- Comment #3 from nsz at gcc dot gnu.org ---
currently --enable-gnu-indirect-function enables its use in gcc target libs
like libatomic which breaks if the libc has no support for it.
(In reply to Florian Weimer from comment #2)
> (In reply to nsz from comment #1)
> > the ifunc abi still has many problems and i don't think it's possible to
> > detect
> > dynamic linker support for cross compilation so if it is enabled do it only
> > if
> > the default libc is glibc (e.g. on linux musl, bionic and uclibc does not
> > plan to implement it).
> 
> Will GCC generate IFUNCs although the attribute is never used?
> 
> If it is harmless to enable it, I'd suggest to do so unconditionally, so
> that people can cross-build glibc on any Linux system using the system
> compiler.

currently --enable-gnu-indirect-function enables ifuncs
in gcc target libs like libatomic, which breaks if the
libc has no support for it (i think this is a significant
abi commitment between gcc and libc which is not justified).