[lldb] Make the system log a NOOP on non-Darwin platforms

As discussed in llvm#111911, we have consensus that as it stands, the system
log is only meaningful on Darwin and that by default it should be a NOOP
on other platforms.

(cherry picked from commit cc13d4f)

Author: JDevlieghere

lldb/source/Host/common/Host.cpp

@@ -89,31 +89,12 @@ using namespace lldb;
 using namespace lldb_private;
 
 #if !defined(__APPLE__)
-#if !defined(_WIN32)
-#include <syslog.h>
-void Host::SystemLog(Severity severity, llvm::StringRef message) {
-  static llvm::once_flag g_openlog_once;
-  llvm::call_once(g_openlog_once, [] {
-    openlog("lldb", LOG_CONS | LOG_PID | LOG_NDELAY, LOG_USER);
-  });
-  int level = LOG_DEBUG;
-  switch (severity) {
-  case lldb::eSeverityInfo:
-    level = LOG_INFO;
-    break;
-  case lldb::eSeverityWarning:
-    level = LOG_WARNING;
-    break;
-  case lldb::eSeverityError:
-    level = LOG_ERR;
-    break;
-  }
-  syslog(level, "%s", message.data());
-}
-#else
+// The system log is currently only meaningful on Darwin, where this means
+// os_log. The meaning of a "system log" isn't as clear on other platforms, and
+// therefore we don't providate a default implementation. Vendors are free to
+// to implement this function if they have a use for it.
 void Host::SystemLog(Severity severity, llvm::StringRef message) {}
 #endif
-#endif
 
 #if !defined(__APPLE__) && !defined(_WIN32)
 static thread_result_t