bmcweb: Fix a bunch of warnings

bmcweb classically has not taken a strong opinion on warnings.  With
this commit, that policy is changing, and bmcweb will invoke the best
warnings we are able to enable, and turn on -Werror for all builds.

This is intended to reduce the likelihood of hard-to-debug situations
that the compiler coulve caught early on.

Change-Id: I57474410821e82666b3a108cfd0db7d070e8900a
Signed-off-by: Ed Tanous <ed@tanous.net>
diff --git a/include/dbus_monitor.hpp b/include/dbus_monitor.hpp
index 1b82697..cddafc8 100644
--- a/include/dbus_monitor.hpp
+++ b/include/dbus_monitor.hpp
@@ -150,7 +150,7 @@
             nlohmann::json::iterator paths = j.find("paths");
             if (paths != j.end())
             {
-                int interfaceCount = thisSession.interfaces.size();
+                size_t interfaceCount = thisSession.interfaces.size();
                 if (interfaceCount == 0)
                 {
                     interfaceCount = 1;