Use #pragma weak to prevent multiple definitions of g_client

The variable g_client is defined in both
erpc_arbitrated_client_setup.cpp and erpc_client_setup.cpp. #pragma weak
is used to avoid a linker failure due to multiple definitions of this
variable.

Resolves: #113

Author: dpfrey

erpc_c/setup/erpc_arbitrated_client_setup.cpp

@@ -32,8 +32,8 @@ using namespace erpc;
 
 // global client variables
 static ManuallyConstructed<ArbitratedClientManager> s_client;
-extern ClientManager *g_client;
-ClientManager *g_client = NULL;
+#pragma weak g_client
+ClientManager *g_client;
 
 static ManuallyConstructed<BasicCodecFactory> s_codecFactory;
 static ManuallyConstructed<TransportArbitrator> s_arbitrator;

erpc_c/setup/erpc_client_setup.cpp

@@ -30,8 +30,8 @@ using namespace erpc;
 
 // global client variables
 static ManuallyConstructed<ClientManager> s_client;
-extern ClientManager *g_client;
-ClientManager *g_client = NULL;
+#pragma weak g_client
+ClientManager *g_client;
 static ManuallyConstructed<BasicCodecFactory> s_codecFactory;
 static ManuallyConstructed<Crc16> s_crc16;