powerpc: Move cache line size to rtld_global_ro

GCC 10.0 enabled -fno-common by default and this started to point that
__cache_line_size had been implemented in 2 different places: loader and
libc.

In order to avoid this duplication, the libc variable has been removed
and the loader variable is moved to rtld_global_ro.

File sysdeps/unix/sysv/linux/powerpc/dl-auxv.h has been added in order
to reuse code for both static and dynamic linking scenarios.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

sysdeps/unix/sysv/linux/powerpc/dl-auxv.h

@@ -0,0 +1,30 @@
+/* Auxiliary vector processing.  Linux/PPC version.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <ldsodefs.h>
+
+#if IS_IN (libc) && !defined SHARED
+int GLRO(dl_cache_line_size);
+#endif
+
+/* Scan the Aux Vector for the "Data Cache Block Size" entry and assign it
+   to dl_cache_line_size.  */
+#define DL_PLATFORM_AUXV						      \
+      case AT_DCACHEBSIZE:						      \
+	GLRO(dl_cache_line_size) = av->a_un.a_val;			      \
+	break;