gn: Fix missing dependencies

Change-Id: Ic1878cb87aab2a29fdf1aac39d2108e39c670860
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/60181
Pigweed-Auto-Submit: Rob Mohr <mohrr@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Auto-Submit <auto-submit@pigweed.google.com.iam.gserviceaccount.com>
diff --git a/pw_boot_cortex_m/BUILD.gn b/pw_boot_cortex_m/BUILD.gn
index 8d1e020..0bebd2d 100644
--- a/pw_boot_cortex_m/BUILD.gn
+++ b/pw_boot_cortex_m/BUILD.gn
@@ -54,6 +54,9 @@
     ]
     sources = [ "core_init.c" ]
   }
+} else {
+  group("armv7m") {
+  }
 }
 
 if (pw_boot_BACKEND == "$dir_pw_boot_cortex_m:armv8m") {
@@ -68,6 +71,9 @@
     ]
     sources = [ "core_init.c" ]
   }
+} else {
+  group("armv8m") {
+  }
 }
 
 pw_doc_group("docs") {
diff --git a/pw_multisink/BUILD.gn b/pw_multisink/BUILD.gn
index 4769767..bc64c81 100644
--- a/pw_multisink/BUILD.gn
+++ b/pw_multisink/BUILD.gn
@@ -90,15 +90,13 @@
   deps = [ ":pw_multisink" ]
 }
 
-if (pw_thread_THREAD_BACKEND == "$dir_pw_thread_stl:thread") {
-  pw_source_set("stl_test_thread") {
-    sources = [ "stl_test_thread.cc" ]
-    deps = [
-      ":test_thread",
-      "$dir_pw_thread:thread",
-      "$dir_pw_thread_stl:thread",
-    ]
-  }
+pw_source_set("stl_test_thread") {
+  sources = [ "stl_test_thread.cc" ]
+  deps = [
+    ":test_thread",
+    "$dir_pw_thread:thread",
+    "$dir_pw_thread_stl:thread",
+  ]
 }
 
 pw_test("stl_multisink_threaded_test") {
diff --git a/pw_thread/BUILD.gn b/pw_thread/BUILD.gn
index ad745ac..69a9c86 100644
--- a/pw_thread/BUILD.gn
+++ b/pw_thread/BUILD.gn
@@ -129,28 +129,26 @@
   ]
 }
 
-if (pw_thread_THREAD_BACKEND != "") {
-  pw_source_set("test_threads") {
-    public_configs = [ ":public_include_path" ]
-    public = [ "public/pw_thread/test_threads.h" ]
-    public_deps = [ ":thread" ]
-  }
+pw_source_set("test_threads") {
+  public_configs = [ ":public_include_path" ]
+  public = [ "public/pw_thread/test_threads.h" ]
+  public_deps = [ ":thread" ]
+}
 
-  # To instantiate this facade test based on a selected backend to provide
-  # test_threads you can create a pw_test target which depends on this
-  # pw_source_set and a pw_source_set which provides the implementation of
-  # test_threads. See "$dir_pw_thread_stl:thread_backend_test" as an example.
-  pw_source_set("thread_facade_test") {
-    sources = [ "thread_facade_test.cc" ]
-    deps = [
-      ":id",
-      ":sleep",
-      ":test_threads",
-      ":thread",
-      "$dir_pw_sync:binary_semaphore",
-      dir_pw_unit_test,
-    ]
-  }
+# To instantiate this facade test based on a selected backend to provide
+# test_threads you can create a pw_test target which depends on this
+# pw_source_set and a pw_source_set which provides the implementation of
+# test_threads. See "$dir_pw_thread_stl:thread_backend_test" as an example.
+pw_source_set("thread_facade_test") {
+  sources = [ "thread_facade_test.cc" ]
+  deps = [
+    ":id",
+    ":sleep",
+    ":test_threads",
+    ":thread",
+    "$dir_pw_sync:binary_semaphore",
+    dir_pw_unit_test,
+  ]
 }
 
 pw_test("yield_facade_test") {
diff --git a/pw_work_queue/BUILD.gn b/pw_work_queue/BUILD.gn
index fd10b8d..08fd679 100644
--- a/pw_work_queue/BUILD.gn
+++ b/pw_work_queue/BUILD.gn
@@ -67,15 +67,13 @@
   tests = [ ":stl_work_queue_test" ]
 }
 
-if (pw_thread_THREAD_BACKEND == "$dir_pw_thread_stl:thread") {
-  pw_source_set("stl_test_thread") {
-    sources = [ "stl_test_thread.cc" ]
-    deps = [
-      ":test_thread",
-      "$dir_pw_thread:thread",
-      "$dir_pw_thread_stl:thread",
-    ]
-  }
+pw_source_set("stl_test_thread") {
+  sources = [ "stl_test_thread.cc" ]
+  deps = [
+    ":test_thread",
+    "$dir_pw_thread:thread",
+    "$dir_pw_thread_stl:thread",
+  ]
 }
 
 pw_test("stl_work_queue_test") {