LibCore: Add wrapper for signal()

Userland/Libraries/LibCore/System.cpp

@@ -8,6 +8,7 @@
 #include <AK/String.h>
 #include <LibCore/System.h>
 #include <LibSystem/syscall.h>
+#include <cstring>
 #include <fcntl.h>
 #include <stdarg.h>
 #include <sys/ioctl.h>
@@ -115,6 +116,18 @@ ErrorOr<void> sigaction(int signal, struct sigaction const* action, struct sigac
     return {};
 }
 
+#ifdef __APPLE__
+ErrorOr<sig_t> signal(int signal, sig_t handler)
+#else
+ErrorOr<sighandler_t> signal(int signal, sighandler_t handler)
+#endif
+{
+    auto old_handler = ::signal(signal, handler);
+    if (old_handler == SIG_ERR)
+        return Error::from_syscall("signal"sv, -errno);
+    return old_handler;
+}
+
 ErrorOr<struct stat> fstat(int fd)
 {
     struct stat st = {};

Userland/Libraries/LibCore/System.h

@@ -31,6 +31,11 @@ ErrorOr<void> mount(int source_fd, StringView target, StringView fs_type, int fl
 #endif
 
 ErrorOr<void> sigaction(int signal, struct sigaction const* action, struct sigaction* old_action);
+#ifdef __APPLE__
+ErrorOr<sig_t> signal(int signal, sig_t handler);
+#else
+ErrorOr<sighandler_t> signal(int signal, sighandler_t handler);
+#endif
 ErrorOr<struct stat> fstat(int fd);
 ErrorOr<int> fcntl(int fd, int command, ...);
 ErrorOr<void*> mmap(void* address, size_t, int protection, int flags, int fd, off_t, size_t alignment = 0, StringView name = {});