title: libpthread.so.0: error adding symbols: DSO missing from command line
body: <p>When I'm compiling openvswitch-1.5.0, I've encountered the following compile error:</p>
  
  <pre><code> gcc -Wstrict-prototypes -Wall -Wno-sign-compare -Wpointer-arith
       -Wdeclaration-after-statement -Wformat-security -Wswitch-enum -Wunused-parameter -Wstrict-aliasing -Wbad-function-cast -Wcast-align -Wstrict-prototypes -Wold-style-definition -Wmissing-prototypes -Wmissing-field-initializers -Wno-override-init  -g -O2 -export-dynamic ***-lpthread***  -o utilities/ovs-dpctl utilities/ovs-dpctl.o lib/libopenvswitch.a
   /home/jyyoo/src/dpdk/build/lib/librte_eal.a
   /home/jyyoo/src/dpdk/build/lib/libethdev.a
   /home/jyyoo/src/dpdk/build/lib/librte_cmdline.a
   /home/jyyoo/src/dpdk/build/lib/librte_hash.a
   /home/jyyoo/src/dpdk/build/lib/librte_lpm.a
   /home/jyyoo/src/dpdk/build/lib/librte_mbuf.a
   /home/jyyoo/src/dpdk/build/lib/librte_ring.a
   /home/jyyoo/src/dpdk/build/lib/librte_mempool.a
   /home/jyyoo/src/dpdk/build/lib/librte_malloc.a -lrt -lm 
       /usr/bin/ld: /home/jyyoo/src/dpdk/build/lib/librte_eal.a(eal.o): undefined reference
       to symbol 'pthread_create@@GLIBC_2.2.5'
       /lib/x86_64-linux-gnu/libpthread.so.0: error adding symbols: DSO missing from 
       command line
  </code></pre>
  
  <p>If I try to see the symbols of <code>libpthread</code>, it looks fine.</p>
  
  <pre><code>$ readelf -s /lib/x86_64-linux-gnu/libpthread.so.0 | grep pthread_create
     199: 0000000000008220  2814 FUNC    GLOBAL DEFAULT   13 pthread_create@@GLIBC_2.2.5
     173: 0000000000008220  2814 FUNC    LOCAL  DEFAULT   13 __pthread_create_2_1
     462: 0000000000008220  2814 FUNC    GLOBAL DEFAULT   13 pthread_create@@GLIBC_2.2
  </code></pre>
  
  <p>Could you give any hints or pointers?</p>