Enable ifunc attribute by default for SPARC GNU/Linux.

Enable ifunc attribute by default for SPARC GNU/Linux.

Similar to other architectures with IFUNC binutils/glibc support, this
patch enables the ifunc attribute for SPARC GNU/Linux.  This is needed
for building glibc with the current checks on IFUNC resolver types
(and use of the attribute in glibc rather than manually created IFUNCs
is beneficial anyway because it results in better debug info).

Tested compilation of glibc with build-many-glibcs.py.  I have not run
the GCC tests for SPARC.

	* config.gcc (default_gnu_indirect_function): Default to yes for
	sparc*-*-linux* with glibc.

From-SVN: r253253