Merge bitcoin/bitcoin#30327: build: Drop redundant sys/sysctl.h header check

c0b5ea5 build: Drop redundant `sys/sysctl.h` header check (Hennadii Stepanov)

Pull request description:

  The `AC_CHECK_HEADERS` macro defines `HAVE_SYS_SYSCTL_H` if the `sys/sysctl.h` header is found. However, in the source code, this header is guarded by `HAVE_SYSCTL` and `HAVE_SYSCTL_ARND` macros, which have their own checks. Since `HAVE_SYS_SYSCTL_H` is not used, we can skip the `AC_CHECK_HEADERS(... sys/sysctl.h ...)` check.

ACKs for top commit:
  laanwj:
    ACK c0b5ea5
  fanquake:
    ACK c0b5ea5 - we could got the other way, and add nested #defs, but that doesn't seem worthwhile.

Tree-SHA512: 73bc4bbfc5c457cd2c38e40f8e57d2a70c06ef661d76d4148d683d262be45b9405b8cda1958ac611c312ca7d9e2f9624cf2cac1b61f1008af0856875c62f0eac

Author: fanquake

configure.ac

@@ -897,7 +897,7 @@ if test "$TARGET_OS" = "darwin"; then
   AX_CHECK_LINK_FLAG([-Wl,-fixup_chains], [HARDENED_LDFLAGS="$HARDENED_LDFLAGS -Wl,-fixup_chains"], [], [$LDFLAG_WERROR])
 fi
 
-AC_CHECK_HEADERS([sys/select.h sys/prctl.h sys/sysctl.h vm/vm_param.h sys/vmmeter.h sys/resources.h])
+AC_CHECK_HEADERS([sys/select.h sys/prctl.h vm/vm_param.h sys/vmmeter.h sys/resources.h])
 
 AC_CHECK_DECLS([getifaddrs, freeifaddrs],[CHECK_SOCKET],,
     [#include <sys/types.h>