Make cpptest build on Ubuntu (#2798)

CMakeLists.txt

@@ -232,7 +232,7 @@ if(GTEST_LIB)
     add_executable(${__execname} ${__srcpath})
     list(APPEND TEST_EXECS ${__execname})
     target_link_libraries(${__execname}
-      tvm ${GTEST_LIB} pthread)
+      tvm ${GTEST_LIB} pthread dl)
     set_target_properties(${__execname} PROPERTIES EXCLUDE_FROM_ALL 1)
     set_target_properties(${__execname} PROPERTIES EXCLUDE_FROM_DEFAULT_BUILD 1)
   endforeach()

docs/contribute/pull_request.rst

@@ -62,14 +62,15 @@ C++
   TVM_ROOT=`pwd`
 
   # you need to install google test first, gtest will be installed to $TVM_ROOT/lib
+  apt-get install -y libgtest-dev
   CACHE_PREFIX=. make -f 3rdparty/dmlc-core/scripts/packages.mk gtest
 
   mkdir build
   cd build
-  GTEST_LIB=$TVM_ROOT/lib cmake ..
-  make cpptest -j
+  GTEST_LIB=$TVM_ROOT/lib cmake -DUSE_LLVM=ON ..
+  make cpptest -j$(nproc)
   for test in *_test; do
-    ./$test || exit -1
+    ./$test
   done
 
 Python