Fix detection of ARMv7 and ARM64 CPU features on FreeBSD

OpenSSL assumes AT_HWCAP = 16 (as on Linux), but on FreeBSD AT_HWCAP = 25
Switch to using AT_HWCAP, and setting it to 16 if it is not defined.

OpenSSL calls elf_auxv_info() with AT_CANARY which returns ENOENT
resulting in all ARM acceleration features being disabled.

CLA: trivial

Reviewed-by: Ben Kaduk <kaduk@mit.edu>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17082)
diff --git a/crypto/armcap.c b/crypto/armcap.c
index 62e166a..5b45a9d 100644
--- a/crypto/armcap.c
+++ b/crypto/armcap.c
@@ -112,20 +112,23 @@
  * ARM puts the feature bits for Crypto Extensions in AT_HWCAP2, whereas
  * AArch64 used AT_HWCAP.
  */
+# ifndef AT_HWCAP
+#  define AT_HWCAP               16
+# endif
+# ifndef AT_HWCAP2
+#  define AT_HWCAP2              26
+# endif
 # if defined(__arm__) || defined (__arm)
-#  define HWCAP                  16
-                                  /* AT_HWCAP */
+#  define HWCAP                  AT_HWCAP
 #  define HWCAP_NEON             (1 << 12)
 
-#  define HWCAP_CE               26
-                                  /* AT_HWCAP2 */
+#  define HWCAP_CE               AT_HWCAP2
 #  define HWCAP_CE_AES           (1 << 0)
 #  define HWCAP_CE_PMULL         (1 << 1)
 #  define HWCAP_CE_SHA1          (1 << 2)
 #  define HWCAP_CE_SHA256        (1 << 3)
 # elif defined(__aarch64__)
-#  define HWCAP                  16
-                                  /* AT_HWCAP */
+#  define HWCAP                  AT_HWCAP
 #  define HWCAP_NEON             (1 << 1)
 
 #  define HWCAP_CE               HWCAP