Fix building crc32_arm64 on NetBSD/aarch64

pmull_supported is not necessarily defined before crc32c_aarch64
Signed-off-by: Nia Alarie <nia@NetBSD.org>

mysys/crc32/crc32_arm64.c

@@ -2,13 +2,13 @@
 #include <string.h>
 #include <stdint.h>
 
+static int pmull_supported;
+
 #if defined(HAVE_ARMV8_CRC)
 
 #if defined(__APPLE__)
 #include <sys/sysctl.h>
 
-static int pmull_supported;
-
 int crc32_aarch64_available(void)
 {
   int ret;
@@ -48,8 +48,6 @@ static unsigned long getauxval(unsigned int key)
 # define HWCAP_PMULL (1 << 4)
 #endif
 
-static int pmull_supported;
-
 /* ARM made crc32 default from ARMv8.1 but optional in ARMv8A
  * Runtime check API.
  */