Build failure - link issues

[uday-cb]

This doesn't build out of the box on FC31 (gcc (GCC) 9.3.1 20200317 (Red Hat 9.3.1-1)). It looks like -lpthread in missing from the link flags.

[ 72%] Built target test_sqlite++
/usr/bin/cmake -E cmake_link_script CMakeFiles/clang-tags-server.dir/link.txt --verbose=1
/usr/lib64/ccache/c++    -rdynamic CMakeFiles/clang-tags-server.dir/main.cxx.o CMakeFiles/clang-tags-server.dir/request/request.cxx.o CMakeFiles/clang-tags-server.dir/compilationDatabase.cxx.o CMakeFiles/clang-tags-server.dir/index.cxx.o CMakeFiles/clang-tags-server.dir/findDefinition.cxx.o CMakeFiles/clang-tags-server.dir/grep.cxx.o CMakeFiles/clang-tags-server.dir/complete.cxx.o  -o clang-tags-server  -lboost_system -ljsoncpp -lclang -lsqlite3 libsqlite++.a libclang++.a libgetopt++.a 
/usr/bin/ld: CMakeFiles/clang-tags-server.dir/main.cxx.o: undefined reference to symbol 'pthread_join@@GLIBC_2.2.5'
/usr/bin/ld: /usr/lib64/libpthread.so.0: error adding symbols: DSO missing from command line
collect2: error: ld returned 1 exit status
make[2]: *** [CMakeFiles/clang-tags-server.dir/build.make:198: clang-tags-server] Error 1
make[2]: Leaving directory '/home/uday/Downloads/clang-tags'
make[1]: *** [CMakeFiles/Makefile2:301: CMakeFiles/clang-tags-server.dir/all] Error 2
make[1]: Leaving directory '/home/uday/Downloads/clang-tags'
make: *** [Makefile:158: all] Error 2

Adding it makes it fine.