Switch <elf.h> over to linux uapi under the covers.

Remove the linker's reliance on BSD cruft and use the glibc-style
ElfW macro. (Other code too, but the linker contains the majority
of the code that needs to work for Elf32 and Elf64.)

All platforms need dl_iterate_phdr_static, so it doesn't make sense
to have that part of the per-architecture configuration.

Bug: 12476126
Change-Id: I1d7f918f1303a392794a6cd8b3512ff56bd6e487
diff --git a/libc/private/bionic_auxv.h b/libc/private/bionic_auxv.h
index 69c5341..53fcc49 100644
--- a/libc/private/bionic_auxv.h
+++ b/libc/private/bionic_auxv.h
@@ -29,11 +29,12 @@
 #define _PRIVATE_BIONIC_AUXV_H_
 
 #include <elf.h>
+#include <link.h>
 #include <sys/cdefs.h>
 
 __BEGIN_DECLS
 
-extern Elf_auxv_t* __libc_auxv;
+extern ElfW(auxv_t)* __libc_auxv;
 
 __END_DECLS