title: error during making GTest
body: <p>I was trying to set up GTest environment on my Ubuntu machine. but while making the GTest to get the library, i get the following error...</p>
  
  <pre><code>som@som-VPCEH25EN:~/Workspace/CPP/gtest-1.6.0/make$ make
  g++ -I../include -g -Wall -Wextra -lpthread sample1.o sample1_unittest.o gtest_main.a -o sample1_unittest
  gtest_main.a(gtest-all.o): In function `~ThreadLocal':
  /home/som/Workspace/CPP/gtest-1.6.0/make/../include/gtest/internal/gtest-port.h:1336: undefined reference to `pthread_getspecific'
  /home/som/Workspace/CPP/gtest-1.6.0/make/../include/gtest/internal/gtest-port.h:1340: undefined reference to `pthread_key_delete'
  /home/som/Workspace/CPP/gtest-1.6.0/make/../include/gtest/internal/gtest-port.h:1336: undefined reference to `pthread_getspecific'
  /home/som/Workspace/CPP/gtest-1.6.0/make/../include/gtest/internal/gtest-port.h:1340: undefined reference to `pthread_key_delete'
  gtest_main.a(gtest-all.o): In function `testing::internal::ThreadLocal&lt;std::vector&lt;testing::internal::TraceInfo, std::allocator&lt;testing::internal::TraceInfo&gt; &gt; &gt;::GetOrCreateValue() const':
  /home/som/Workspace/CPP/gtest-1.6.0/make/../include/gtest/internal/gtest-port.h:1372: undefined reference to `pthread_getspecific'
  /home/som/Workspace/CPP/gtest-1.6.0/make/../include/gtest/internal/gtest-port.h:1379: undefined reference to `pthread_setspecific'
  gtest_main.a(gtest-all.o): In function `testing::internal::ThreadLocal&lt;testing::TestPartResultReporterInterface*&gt;::CreateKey()':
  /home/som/Workspace/CPP/gtest-1.6.0/make/../include/gtest/internal/gtest-port.h:1365: undefined reference to `pthread_key_create'
  gtest_main.a(gtest-all.o): In function `testing::internal::ThreadLocal&lt;std::vector&lt;testing::internal::TraceInfo, std::allocator&lt;testing::internal::TraceInfo&gt; &gt; &gt;::CreateKey()':
  /home/som/Workspace/CPP/gtest-1.6.0/make/../include/gtest/internal/gtest-port.h:1365: undefined reference to `pthread_key_create'
  gtest_main.a(gtest-all.o): In function `testing::internal::ThreadLocal&lt;testing::TestPartResultReporterInterface*&gt;::GetOrCreateValue() const':
  /home/som/Workspace/CPP/gtest-1.6.0/make/../include/gtest/internal/gtest-port.h:1372: undefined reference to `pthread_getspecific'
  /home/som/Workspace/CPP/gtest-1.6.0/make/../include/gtest/internal/gtest-port.h:1379: undefined reference to `pthread_setspecific'
  collect2: ld returned 1 exit status
  make: *** [sample1_unittest] Error 1
  </code></pre>