Merge bitcoin/bitcoin#23045: build: Restrict check for CRC32C intrinsic to aarch64

f2747d1 build: Restrict check for CRC32C intrinsic to aarch64 (W. J. van der Laan)

Pull request description:

  `crc32c`'s hardware accelerated code doesn't handle ARM 32-bit at all, but only 64-bit. Make the check in `configure.ac` check for this architecture explicitly. This change does not affect non-ARM architectures.

  For the release binaries, the current `configure.ac` check happens to work: it enables it on aarch64 but disables it for armhf. However some combination of compiler version and settings can cause this check to succeed on armhf (as reported on IRC). So make the 64-bit platform requirement explicit.

  (details: while the check already explicitly checks the `__crc32d` intrinsic, which strictly doesn't exist on 32-bit ARM, this is not enough! gcc happens to helpfully emulate it:
  > These built-in intrinsics for the ARMv8-A CRC32 extension are available when the -march=armv8-a+crc switch is used "uint32_t __crc32d (uint32_t, uint64_t)" Form of expected instruction(s): Two crc32w r0, r0, r0 instructions for AArch32

  )

ACKs for top commit:
  luke-jr:
    re-tACK f2747d1
  jarolrod:
    ACK f2747d1

Tree-SHA512: e5f05f05eeec310ac42685621d86862735586be66dc378db404ec9414ac5aaea7c53d76d76d875b15b11924eee6714076120c07b077183fd7af898704fd81823

Author: laanwj

configure.ac

@@ -568,13 +568,17 @@ AX_CHECK_COMPILE_FLAG([-march=armv8-a+crc+crypto],[[ARM_CRC_CXXFLAGS="-march=arm
 
 TEMP_CXXFLAGS="$CXXFLAGS"
 CXXFLAGS="$CXXFLAGS $ARM_CRC_CXXFLAGS"
-AC_MSG_CHECKING(for ARM CRC32 intrinsics)
+AC_MSG_CHECKING(for AArch64 CRC32 intrinsics)
 AC_COMPILE_IFELSE([AC_LANG_PROGRAM([[
     #include <arm_acle.h>
     #include <arm_neon.h>
   ]],[[
+#ifdef __aarch64__
     __crc32cb(0, 0); __crc32ch(0, 0); __crc32cw(0, 0); __crc32cd(0, 0);
     vmull_p64(0, 0);
+#else
+#error "crc32c library does not support hardware acceleration on 32-bit ARM"
+#endif
   ]])],
  [ AC_MSG_RESULT(yes); enable_arm_crc=yes; ],
  [ AC_MSG_RESULT(no)]