Fix "terminate called after throwing an instance of 'std::system_error'"

This is a re-fix.  The missing pthread lib was fixed in 469a61f044, but then unfixed in 06fc879371.

lint/CMakeLists.txt

@@ -3,3 +3,7 @@ project(peglint)
 include_directories(..)
 add_definitions("-std=c++11")
 add_executable(peglint peglint.cc)
+
+if(CMAKE_SYSTEM_NAME STREQUAL "Linux")
+  target_link_libraries(peglint pthread)
+endif()