Make C++ alarm class usable and testable - there were some build issues and
it was not actually even included in the library or the test suite.
diff --git a/tools/doxygen/Doxyfile.c++.internal b/tools/doxygen/Doxyfile.c++.internal
index bd724d8..6135463 100644
--- a/tools/doxygen/Doxyfile.c++.internal
+++ b/tools/doxygen/Doxyfile.c++.internal
@@ -854,6 +854,7 @@
src/cpp/client/credentials.cc \
src/cpp/client/generic_stub.cc \
src/cpp/client/insecure_credentials.cc \
+src/cpp/common/alarm.cc \
src/cpp/common/call.cc \
src/cpp/common/channel_arguments.cc \
src/cpp/common/completion_queue.cc \