correct the syscall return type

Long size syscall return values such as shmat()'s and lseek()'s are
broken, because lower 32 bits are only returned.

executer/user/mcexec.c

@@ -825,7 +825,7 @@ int main(int argc, char **argv)
 
 
 void do_syscall_return(int fd, int cpu,
-                       int ret, int n, unsigned long src, unsigned long dest,
+                       long ret, int n, unsigned long src, unsigned long dest,
                        unsigned long sz)
 {
 	struct syscall_ret_desc desc;

kernel/include/syscall.h

@@ -207,7 +207,7 @@ struct syscall_params {
 
 #define SYSCALL_FOOTER return do_syscall(&request, ctx, ihk_mc_get_processor_id())
 
-extern int do_syscall(struct syscall_request *req, ihk_mc_user_context_t *ctx, int cpu);
+extern long do_syscall(struct syscall_request *req, ihk_mc_user_context_t *ctx, int cpu);
 extern int obtain_clone_cpuid();
 extern long syscall_generic_forwarding(int n, ihk_mc_user_context_t *ctx);
 

kernel/syscall.c

@@ -151,7 +151,7 @@ static void send_syscall(struct syscall_request *req, int cpu)
 }
 
 
-int do_syscall(struct syscall_request *req, ihk_mc_user_context_t *ctx, int cpu)
+long do_syscall(struct syscall_request *req, ihk_mc_user_context_t *ctx, int cpu)
 {
 	struct syscall_response *res;
 	struct syscall_request req2 IHK_DMA_ALIGN;