Enable the glStringMarker logger when available

glStringMarker is usually only available when running under some
kind of GL debugger, and can be used to insert strings into the
GL command string. Writing logs using it can be useful, since it
lets us correspond GL calls with what happens in compton.

More info about the extension can be found here:

https://www.khronos.org/registry/OpenGL/extensions/GREMEDY/GREMEDY_string_marker.txt

Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>

src/compton.c

@@ -2953,6 +2953,14 @@ session_init(session_t *ps_old, int argc, char **argv) {
     exit(0);
   }
 
+  if (bkend_use_glx(ps)) {
+    auto glx_logger = glx_string_marker_logger_new();
+    if (glx_logger) {
+      log_info("Enabling gl string marker");
+      log_add_target_tls(glx_logger);
+    }
+  }
+
   // Initialize software optimization
   if (ps->o.sw_opti)
     ps->o.sw_opti = swopti_init(ps);