build: enable and fix -Wshadow

Shadow names can be prone to bugs.  Enable the warning to avoid them in
the future.  Tested by building and running the unit tests.

Change-Id: Ic3227675f4ff40d266ae2a60c66c894f16e5888e
Signed-off-by: Brad Bishop <bradbish@qti.qualcomm.com>
diff --git a/fail-monitor/monitor.hpp b/fail-monitor/monitor.hpp
index 65bb810..7512474 100644
--- a/fail-monitor/monitor.hpp
+++ b/fail-monitor/monitor.hpp
@@ -45,12 +45,12 @@
      *
      * @param[in] sourceUnit - the source unit
      * @param[in] targetUnit - the target unit
-     * @param[in] action - the action to run on the target
+     * @param[in] targetAction - the action to run on the target
      */
     Monitor(const std::string& sourceUnit, const std::string& targetUnit,
-            Action action) :
+            Action targetAction) :
         bus(sdbusplus::bus::new_default()), source(sourceUnit),
-        target(targetUnit), action(action)
+        target(targetUnit), action(targetAction)
     {}
 
     /**