build: fix -Wmissing-variable-declarations

This helps make the author's original intent clear.  Tested by building
and running the unit tests with clang.

Change-Id: Iaf0aca72b5a8cc931bcb84c27df1c55d2f438dda
Signed-off-by: Brad Bishop <bradbish@qti.qualcomm.com>
diff --git a/src/test/util/asio_server_class.hpp b/src/test/util/asio_server_class.hpp
index 9526375..fe30e46 100644
--- a/src/test/util/asio_server_class.hpp
+++ b/src/test/util/asio_server_class.hpp
@@ -4,7 +4,7 @@
 #include <sdbusplus/asio/object_server.hpp>
 
 /* @brief Will contain path and name of test application */
-const char* appname = program_invocation_name;
+inline const char* appname = program_invocation_name;
 
 #include <gtest/gtest.h>
 /** @class AsioServerClassTest