libxl: use LOG instead of LIBXL__LOG in libxl_utils.c

To conform to the new coding style, replace the invocation of
LIBXL__LOG in the function libxl_pipe() in the file libxl_utils.c
with an invocation of LOG. Create a local libxl__gc gc* for LOG
to use by invoking GC_INIT(ctx) at the top of the function, and
clean it up by invoking GC_FREE at the exit. Create a variable,
ret, to consolidate exits in one place and avoid invoking GC_FREE
twice.

Suggested-by: Ian Campbell <Ian.Campbell@citrix.com>
Signed-off-by: Kelley Nielsen <kelleynnn@gmail.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>

tools/libxl/libxl_utils.c

@@ -478,11 +478,14 @@ int libxl__remove_directory(libxl__gc *gc, const char *dirpath)
 
 int libxl_pipe(libxl_ctx *ctx, int pipes[2])
 {
+    GC_INIT(ctx);
+    int ret = 0;
     if (pipe(pipes) < 0) {
-        LIBXL__LOG(ctx, LIBXL__LOG_ERROR, "Failed to create a pipe");
-        return -1;
+        LOG(ERROR, "Failed to create a pipe");
+        ret = -1;
     }
-    return 0;
+    GC_FREE;
+    return ret;
 }
 
 int libxl_uuid_to_device_vtpm(libxl_ctx *ctx, uint32_t domid,