Linux: Consolidate auxiliary vector parsing (redo)

And optimize it slightly.

This is commit 8c8510ab27 revised.

In _dl_aux_init in elf/dl-support.c, use an explicit loop
and -fno-tree-loop-distribute-patterns to avoid memset.

Reviewed-by: Szabolcs Nagy <szabolcs.nagy@arm.com>

sysdeps/unix/sysv/linux/powerpc/dl-support.c

@@ -0,0 +1,4 @@
+#include <elf/dl-support.c>
+
+/* Populated from the auxiliary vector.  */
+int _dl_cache_line_size;