Make powerpc-nofpu __sqrtsf2, __sqrtdf2 compat symbols (bug 18473).

powerpc-nofpu libc exports __sqrtsf2 and __sqrtdf2 symbols.  The
export of these soft-fp symbols is a mistake; they aren't part of the
libgcc interface and GCC will never generate code that calls them.
This patch makes them into compat symbols (no code built for static
libc), moving their sources from the generic soft-fp sources to
sysdeps/powerpc/nofpu (the underlying soft-fp FP_SQRT functionality
remains of use to implement actual sqrt public interfaces, such as
sqrtl / sqrtf128 for which it is used on various platforms, but
__sqrt[sdt]f2 are not such interfaces).

Tested with build-many-glibcs.py for relevant platforms.

	[BZ #18473]
	* soft-fp/sqrttf2.c: Remove file.
	* soft-fp/sqrtdf2.c: Move to ....
	* sysdeps/powerpc/nofpu/sqrtdf2.c: ... here.  Include
	<shlib-compat.h>.
	(__sqrtdf2): Make conditional on
	[SHLIB_COMPAT (libc, GLIBC_2_3_2, GLIBC_2_28)].  Define as compat
	symbol.
	* soft-fp/sqrtsf2.c: Move to ....
	* sysdeps/powerpc/nofpu/sqrtsf2.c: ... here.  Include
	<shlib-compat.h>.
	(__sqrtsf2): Make conditional on
	[SHLIB_COMPAT (libc, GLIBC_2_3_2, GLIBC_2_28)].  Define as compat
	symbol.
	* soft-fp/Makefile (gcc-single-routines): Remove sqrtsf2.
	(gcc-double-routines): Remove sqrtdf2.
	(gcc-quad-routines): Remove sqrttf2.
	* sysdeps/nios2/Makefile [$(subdir) = soft-fp] (sysdep_routines):
	Do not filter out sqrtsf2 and sqrtdf2.
	* sysdeps/powerpc/nofpu/Makefile [$(subdir) = soft-fp]
	(sysdep_routines): Add sqrtsf2 and sqrtdf2.