Move syslog support tests to one place.

example/example.cpp

@@ -108,7 +108,7 @@ void async_example()
 //syslog example (linux/osx/freebsd)
 void syslog_example()
 {
-#if defined (__linux__) || defined(__APPLE__)  || defined(__FreeBSD__)
+#ifdef SPDLOG_ENABLE_SYSLOG
     std::string ident = "spdlog-example";
     auto syslog_logger = spd::syslog_logger("syslog", ident, LOG_PID);
     syslog_logger->warn("This is warning that will end up in syslog.");

include/spdlog/common.h

@@ -37,6 +37,12 @@
 #define DEPRECATED
 #endif
 
+#ifndef SPDLOG_ENABLE_SYSLOG
+#if defined (__linux__) || defined(__APPLE__)  || defined(__FreeBSD__)
+#define SPDLOG_ENABLE_SYSLOG
+#endif
+#endif
+
 
 #include <spdlog/fmt/fmt.h>
 

include/spdlog/details/spdlog_impl.h

@@ -96,7 +96,7 @@ inline std::shared_ptr<spdlog::logger> spdlog::stderr_logger_st(const std::strin
     return create_console_logger(logger_name, sinks::stderr_sink_st::instance(), color);
 }
 
-#if defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__)
+#ifdef SPDLOG_ENABLE_SYSLOG
 // Create syslog logger
 inline std::shared_ptr<spdlog::logger> spdlog::syslog_logger(const std::string& logger_name, const std::string& syslog_ident, int syslog_option)
 {

include/spdlog/sinks/syslog_sink.h

@@ -5,10 +5,11 @@
 
 #pragma once
 
-#if defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__)
+#include <spdlog/common.h>
+
+#ifdef SPDLOG_ENABLE_SYSLOG
 
 #include <spdlog/sinks/sink.h>
-#include <spdlog/common.h>
 #include <spdlog/details/log_msg.h>
 
 #include <array>

include/spdlog/spdlog.h

@@ -98,7 +98,7 @@ std::shared_ptr<logger> stderr_logger_st(const std::string& logger_name, bool co
 //
 // Create and register a syslog logger
 //
-#if defined(__linux__) || defined(__APPLE__) || defined(__FreeBSD__)
+#ifdef SPDLOG_ENABLE_SYSLOG
 std::shared_ptr<logger> syslog_logger(const std::string& logger_name, const std::string& ident = "", int syslog_option = 0);
 #endif