LogLevel enum clashes with syslog.h

[zenonparker]

The LogLevel enum in cppkafka/logging.h doesn't play nicely when syslog.h is included prior to its definition (not surprisingly, based on the comment preceding it).

$ grep "LOG_EMERG" /usr/include/sys/syslog.h
#define LOG_EMERG       0       /* system is unusable */

From cppkafka/logging.h:

 // Based on syslog.h levels
 enum class LogLevel : int {
    LOG_EMERG   = 0,    /* system is unusable */