simple-xinit: Introduce an escaped "--" argument.

For testing xephyr-glamor on top of Xvfb in CI better, I want to be
able to make one command line describing the nested server invocation,
but that means I need to get two simple-xinits to split client/server
on different "--" arguments.

Signed-off-by: Eric Anholt <eric@anholt.net>

hw/kdrive/ephyr/meson.build

@@ -38,7 +38,7 @@ if build_xv
     xephyr_dep += dependency('xcb-xv')
 endif
 
-executable(
+xephyr_server = executable(
     'Xephyr',
     srcs,
     include_directories: [

test/simple-xinit.c

@@ -210,7 +210,13 @@ parse_args(int argc, char **argv,
             continue;
         }
 
-        *next_arg = argv[i];
+        /* A sort of escaped "--" argument so we can nest server
+         * invocations for testing.
+         */
+        if (strcmp(argv[i], "----") == 0)
+            *next_arg = (char *)"--";
+        else
+            *next_arg = argv[i];
         next_arg++;
     }