std.c: Use __sigemptyset14 for sigemptyset on NetBSD

Closes #24344.

Author: alexrp

lib/std/c.zig

@@ -10412,7 +10412,10 @@ pub const sigfillset = switch (native_os) {
 };
 
 pub const sigaddset = private.sigaddset;
-pub const sigemptyset = private.sigemptyset;
+pub const sigemptyset = switch (native_os) {
+    .netbsd => private.__sigemptyset14,
+    else => private.sigemptyset,
+};
 pub const sigdelset = private.sigdelset;
 pub const sigismember = private.sigismember;
 
@@ -11268,6 +11271,7 @@ const private = struct {
     extern "c" fn __msync13(addr: *align(page_size) const anyopaque, len: usize, flags: c_int) c_int;
     extern "c" fn __nanosleep50(rqtp: *const timespec, rmtp: ?*timespec) c_int;
     extern "c" fn __sigaction14(sig: c_int, noalias act: ?*const Sigaction, noalias oact: ?*Sigaction) c_int;
+    extern "c" fn __sigemptyset14(set: ?*sigset_t) c_int;
     extern "c" fn __sigfillset14(set: ?*sigset_t) c_int;
     extern "c" fn __sigprocmask14(how: c_int, noalias set: ?*const sigset_t, noalias oset: ?*sigset_t) c_int;
     extern "c" fn __socket30(domain: c_uint, sock_type: c_uint, protocol: c_uint) c_int;