pw_thread_freertos: Add CMake support

Change-Id: Ie34b4d7e45bd59bb418d682c8bcb581d2a522778
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/79724
Reviewed-by: Keir Mierle <keir@google.com>
Pigweed-Auto-Submit: Ewout van Bekkum <ewout@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/CMakeLists.txt b/CMakeLists.txt
index b33e59e..a6d54f3 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -67,6 +67,7 @@
 add_subdirectory(pw_sys_io EXCLUDE_FROM_ALL)
 add_subdirectory(pw_sys_io_stdio EXCLUDE_FROM_ALL)
 add_subdirectory(pw_system EXCLUDE_FROM_ALL)
+add_subdirectory(pw_thread_freertos EXCLUDE_FROM_ALL)
 add_subdirectory(pw_tokenizer EXCLUDE_FROM_ALL)
 add_subdirectory(pw_trace EXCLUDE_FROM_ALL)
 add_subdirectory(pw_trace_tokenized EXCLUDE_FROM_ALL)