build: add thread sanitizer

We have a cmake option to build Tntcxx with sanitizers. Currently, only
memory and UB sanitizers are used - let's populate the list with thread
sanitizer since we have a test for a multithreaded scenario.

Author: drewdzzz

CMakeLists.txt

@@ -95,7 +95,7 @@ OPTION(TNTCXX_ENABLE_SANITIZERS
     OFF)
 
 IF (TNTCXX_ENABLE_SANITIZERS)
-    SET(SANITIZER_FLAGS "-fsanitize=address")
+    SET(SANITIZER_FLAGS "-fsanitize=address -fsanitize=thread")
     # FIXME(gh-62)
     IF (NOT CMAKE_CXX_COMPILER_ID STREQUAL "AppleClang")
         # The leak sanitizer is not available in AppleClang, see