Use #pragma GCC target to enable CRC in ARM64 hw implementation

Use `#pragma GCC target ("+crc+crypto")` to enable the necessary
features in the ARM64 hardware CRC32c implementation.  This makes
it possible to build it without setting `-march` globally.  This should
work with GCC 6.3+, and Clang 18 (tested via godbolt.org).  Older
versions of Clang may require explicit `-march=` still.

crc32c_arm64.c

@@ -16,6 +16,10 @@
 
 #if defined(IS_ARM) && (defined(__linux__) || defined(linux))
 
+#if defined(__GNUC__)
+# pragma GCC target ("+crc+crypto")
+#endif
+
 #include <stddef.h>
 #include <stdint.h>