powerpc: Remove stpcpy internal clash with IFUNC

powerpc: Remove stpcpy internal clash with IFUNC

Commit 142e0a99530 redirected the internal stpcpy to default powerpc64
implementation by redefining the weak_alias at
sysdeps/powerpc/powerpc64/multiarch/stpcpy-ppc64.c:

  #undef weak_alias
  #define weak_alias(name, aliasname) \
    extern __typeof (__stpcpy_ppc) aliasname \
      __attribute__ ((weak, alias ("__stpcpy_ppc")));

This creates a __GI_stpcpy alias that clashes with the IFUNC symbol in
stpcpy.os.  There is not need to define the default version for internal
version, since ifunc should work internally for powerpc64.  This patch
removes the weak_alias indirection.

Checked on powerpc64le.

	* sysdeps/powerpc/powerpc64/multiarch/stpcpy-ppc64.c (weak_alias):
	Remove redirection to __stpcpy_ppc.