On non-Windows systems, send logs to syslog & stderr.

OpenBTS and YateBTS fork a transceiver sub-process and redirect stderr and
stdout, which effectively hide any bladerf logs. For debugging time-critical
code, printf debugging (or logging) is simple yet practically essential.

host/common/src/log.c

@@ -24,6 +24,9 @@
  */
 #ifdef LOGGING_ENABLED
 #include <log.h>
+#if defined(__linux__)
+#include <syslog.h>
+#endif
 #include <stdio.h>
 #include <stdarg.h>
 
@@ -38,7 +41,11 @@ void log_write(bladerf_log_level level, const char *format, ...)
 
         /* Write the log message */
         va_start(args, format);
+#if !defined(__linux__)
         vfprintf(stderr, format, args);
+#else
+        vsyslog(LOG_USER, format, args);
+#endif
         va_end(args);
     }
 }

host/libraries/libbladeRF/src/bladerf.c

@@ -22,6 +22,9 @@
 #include <stdio.h>
 #include <string.h>
 #include <limits.h>
+#if defined(__linux__)
+#include <syslog.h>
+#endif
 #include "rel_assert.h"
 
 #include "libbladeRF.h"     /* Public API */
@@ -1090,6 +1093,10 @@ const char * bladerf_strerror(int error)
 
 void bladerf_version(struct bladerf_version *version)
 {
+#if !defined(WIN32) && !defined(__CYGWIN__)
+    openlog("bladeRF",
+        LOG_CONS | LOG_NDELAY  | LOG_NOWAIT | LOG_PERROR | LOG_PID, LOG_USER);
+#endif
     version->major = LIBBLADERF_VERSION_MAJOR;
     version->minor = LIBBLADERF_VERSION_MINOR;
     version->patch = LIBBLADERF_VERSION_PATCH;