Move agent_named_pipe_name into its own source file.

It's used by server and client, so it seems silly to have it live in
the client code.

windows/CMakeLists.txt

@@ -1,6 +1,7 @@
 set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR})
 
 add_sources_from_current_dir(utils
+  utils/agent_named_pipe_name.c
   utils/arm_arch_queries.c
   utils/cryptoapi.c
   utils/defaults.c

windows/agent-client.c

@@ -123,17 +123,6 @@ static void wm_copydata_agent_query(strbuf *query, void **out, int *outlen)
         LocalFree(psd);
 }
 
-char *agent_named_pipe_name(void)
-{
-    char *username, *suffix, *pipename;
-    username = get_username();
-    suffix = capi_obfuscate_string("Pageant");
-    pipename = dupprintf("\\\\.\\pipe\\pageant.%s.%s", username, suffix);
-    sfree(username);
-    sfree(suffix);
-    return pipename;
-}
-
 Socket *agent_connect(Plug *plug)
 {
     char *pipename = agent_named_pipe_name();

windows/utils/agent_named_pipe_name.c

@@ -0,0 +1,17 @@
+/*
+ * Return the full pathname of the named pipe Pageant will listen on.
+ * Used by both the Pageant server code and client code.
+ */
+
+#include "putty.h"
+#include "cryptoapi.h"
+
+char *agent_named_pipe_name(void)
+{
+    char *username = get_username();
+    char *suffix = capi_obfuscate_string("Pageant");
+    char *pipename = dupprintf("\\\\.\\pipe\\pageant.%s.%s", username, suffix);
+    sfree(username);
+    sfree(suffix);
+    return pipename;
+}