LibCore: Remove usage of a hardcoded constant in gethostname()

Author: https://github.com/LucasChollet
Commit: 8153282923
Pull-request: https://github.com/SerenityOS/serenity/pull/11880
Reviewed-by: https://github.com/IdanHo
Reviewed-by: https://github.com/mjz19910

Userland/Libraries/LibCore/System.cpp

@@ -10,6 +10,7 @@
 #include <AK/Vector.h>
 #include <LibCore/System.h>
 #include <LibSystem/syscall.h>
+#include <limits.h>
 #include <stdarg.h>
 #include <sys/ioctl.h>
 #include <sys/mman.h>
@@ -25,6 +26,14 @@
 
 namespace Core::System {
 
+#ifndef HOST_NAME_MAX
+#    ifdef __APPLE__
+#        define HOST_NAME_MAX 255
+#    else
+#        define HOST_NAME_MAX 64
+#    endif
+#endif
+
 #ifdef __serenity__
 
 ErrorOr<void> beep()
@@ -336,7 +345,7 @@ ErrorOr<String> ptsname(int fd)
 
 ErrorOr<String> gethostname()
 {
-    char hostname[256];
+    char hostname[HOST_NAME_MAX];
     int rc = ::gethostname(hostname, sizeof(hostname));
     if (rc < 0)
         return Error::from_syscall("gethostname"sv, -errno);