sysutils/cpuid2cpuflags: make the port build and work on ARM

- Replace getauxval(3), a non-standard glibc extension, with
  our native elf_aux_info(3) call
- Return features supported by the specific machine processor
  architecture (uname -p) rather than the hardware platform
  (uname -m), because the latter is too vague on FreeBSD/arm

PR:		258445
Reported by:	pkg-fallout

sysutils/cpuid2cpuflags/files/patch-src_hwcap.c

@@ -0,0 +1,48 @@
+--- src/hwcap.c.orig	2020-07-13 17:14:55 UTC
++++ src/hwcap.c
+@@ -14,13 +14,19 @@
+ #ifdef HAVE_SYS_AUXV_H
+ #	include <sys/auxv.h>
+ #endif
++#ifdef __FreeBSD__
++#include <sys/sysctl.h>
++#else
+ #include <sys/utsname.h>
+-
+-#ifndef __linux__
+-#	error "Platform not supported (only Linux supported at the moment)"
+ #endif
++
+ #ifndef HAVE_GETAUXVAL
+-#	error "Platform not supported (no getauxval())"
++static unsigned long getauxval(int aux)
++{
++	unsigned long auxval = 0;
++	elf_aux_info(aux, &auxval, sizeof(auxval));
++	return auxval;
++}
+ #endif
+
+ #include "hwcap.h"
+@@ -53,9 +59,21 @@ unsigned long get_hwcap2()
+  */
+ char* get_uname_machine()
+ {
++#ifdef __FreeBSD__
++	/**
++	 * Contrary to this code expectation, on FreeBSD/arm, `uname -m'
++	 * is always `arm', so we return more unique `uname -p' instead.
++	 */
++	int mib[] = { CTL_HW, HW_MACHINE_ARCH };
++	static char buf[48];
++	size_t len = sizeof(buf);
++	if (sysctl(mib, 2, &buf, &len, NULL, 0) == 0)
++		return buf;
++#else
+ 	static struct utsname uname_res;
+ 	if (uname(&uname_res) != -1)
+ 		return uname_res.machine;
++#endif
+ 	else
+ 		return NULL;
+ }