rs6000: Remove LINK_OS_EXTRA_SPEC{32,64} from --with-advance-toolchain

rs6000: Remove LINK_OS_EXTRA_SPEC{32,64} from --with-advance-toolchain

Historically this was added to fill gaps from ld.so.cache on early AT
releases. This now are just causing errors and rework. Since AT5.0 the
AT's ld.so is using a correctly configured ld.so.cache and sets the
DT_INTERP to AT's ld.so. This two factors are sufficient for an AT
builded program to get the correct libraries.

GCC congured with --with-advance-toolchain has issues building GlibC
releases because it adds DT_RUNPATH to ld.so and that's unsupported.

2021-11-10  Lucas A. M. Magalhães  <lamm@linux.ibm.com>

gcc/
	* config.gcc (powerpc*-*-*): Remove -rpath from
	--with-advance-toolchain.