linker: add LD_SHOW_AUXV support.
Yes, `od -t d8 /proc/self/auxv` is clever:
```
$ adb shell od -t d8 /proc/self/auxv
0000000 33 488593047552
0000020 51 4720
0000040 16 1155071
0000060 6 4096
0000100 17 100
0000120 3 375971917888
0000140 4 56
0000160 5 12
0000200 7 488593051648
0000220 8 0
0000240 9 375972184064
0000260 11 0
0000300 12 0
0000320 13 0
0000340 14 0
0000360 23 0
0000400 25 549220780840
0000420 26 0
0000440 31 549220786153
0000460 15 549220780856
0000500 0 0
0000520
$
```
But this is a lot easier to read:
```
$ adb shell LD_SHOW_AUXV=1 date
AT_SYSINFO_EHDR 0x7065010000
AT_MINSIGSTKSZ 4720
AT_HWCAP 0b100011001111111111111
AT_PAGESZ 4096
AT_CLKTCK 100
AT_PHDR 0x5c79d60040
AT_PHENT 56
AT_PHNUM 12
AT_BASE 0x7065011000
AT_FLAGS 0
AT_ENTRY 0x5c79da1000
AT_UID 0
AT_EUID 0
AT_GID 0
AT_EGID 0
AT_SECURE 0
AT_RANDOM 0x7ff814eb98
AT_HWCAP2 0
AT_EXECFN "/system/bin/date"
AT_PLATFORM "aarch64"
Tue Aug 22 20:43:22 GMT 2023
```
Test: adb shell LD_SHOW_AUXV=1 date
Change-Id: I51c4e8cbb799eb1dc360c9417cc6f82bebdcda73
diff --git a/linker/linker_auxv.h b/linker/linker_auxv.h
new file mode 100644
index 0000000..c093283
--- /dev/null
+++ b/linker/linker_auxv.h
@@ -0,0 +1,34 @@
+/*
+ * Copyright (C) 2023 The Android Open Source Project
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ * * Redistributions in binary form must reproduce the above copyright
+ * notice, this list of conditions and the following disclaimer in
+ * the documentation and/or other materials provided with the
+ * distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+ * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
+ * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
+ * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
+ * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
+ * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
+ * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+ * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+ * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#pragma once
+
+#include <elf.h>
+#include <link.h>
+
+void ld_show_auxv(ElfW(auxv_t)* auxv);