Switch C++ source files to .cpp extension

Change-Id: I495186b4afd58ec1e5d9d5c6472394f96541d17d
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
diff --git a/Makefile b/Makefile
index 447b129..8652658 100644
--- a/Makefile
+++ b/Makefile
@@ -53,7 +53,7 @@
 $(WHITELIST_SRC) : generate_whitelist.sh $(WHITELIST_CONF)
 	./$^ > $@
 
-%.o: %.C
+%.o: %.cpp
 	$(CXX) -std=c++14 -fpic -c $< $(CXXFLAGS) $(INC_FLAG) $(IPMID_PATH) -o $@
 
 $(LIB_APP): $(LIB_APP_OBJ)