Failure linking when using an extra library - c++

Question

When I build a simple C++ program with glog library (Google's logging library which is not used in the code), I get "undefined reference" errors. When I remove the -lglog from the build command, the link succeeds.
Notice that the library that I added to the link is not used in the code at all and despite that it caused the build to fail. In addition, the glog and log4cpp libraries are supposed to be independent.
Can you explain this unusual behavior?
Environment: Ubuntu 14.04
Code:
//test.cpp
#include "log4cpp/Appender.hh"
#include "log4cpp/FileAppender.hh"
int main() {
log4cpp::Appender *appender;
appender = new log4cpp::FileAppender("default", "program.log");
return 0;
}
Working build command:
$ g++ test.cpp -llog4cpp -lpthread
Failing build command:
$ g++ test.cpp -llog4cpp -lglog -lpthread
//usr/local/lib/liblog4cpp.so: undefined reference to `pthread_key_create'
//usr/local/lib/liblog4cpp.so: undefined reference to `pthread_getspecific'
//usr/local/lib/liblog4cpp.so: undefined reference to `pthread_key_delete'
//usr/local/lib/liblog4cpp.so: undefined reference to `pthread_setspecific'
collect2: error: ld returned 1 exit status
EDIT:
This command also builds successfully:
g++ test.cpp -llog4cpp -lpthread -lglog
This command fails (change the order of libs):
$ g++ test.cpp -llog4cpp -lglog -lpthread
//usr/local/lib/liblog4cpp.so: undefined reference to `pthread_key_create'
//usr/local/lib/liblog4cpp.so: undefined reference to `pthread_getspecific'
//usr/local/lib/liblog4cpp.so: undefined reference to `pthread_key_delete'
//usr/local/lib/liblog4cpp.so: undefined reference to `pthread_setspecific'
collect2: error: ld returned 1 exit status
This succeeds:
$ g++ test.cpp -pthread -llog4cpp
This fails:
$ g++ test.cpp -pthread -llog4cpp -lglog
EDIT 2:
I studied the duplicate suggestions (1) and (2) to find out maybe there's something useful to me there, but it turned out irrelevant because these cases doesn't address the situation where a library that is not used in the code is added to the link and make it fail.
EDIT 3:
The files from my environment (glog libs, log4cpp libs, used log4cpp headers and test.cpp): log_test.zip.