compat.glx-runtime: declare provides= (strong provider claim)

With mcpp's provides= support (mcpp#110), the host-GL passthrough package
explicitly claims fulfilment of opengl.glx.driver / x11.display, so provider
selection (why/doctor/resolution.json) attributes the capabilities to it
rather than to weak capability-listing consumers like compat.glfw.
Backward-compatible: older mcpp ignores the key.

Author: d2learn-org

pkgs/c/compat.glx-runtime.lua

@@ -29,6 +29,7 @@ package = {
             library_dirs = { "mcpp_generated/glx_runtime/lib" },
             dlopen_libs = { "libGLX.so.0", "libGL.so.1", "libGL.so" },
             capabilities = { "x11.display", "opengl.glx.driver" },
+            provides = { "opengl.glx.driver", "x11.display" },
         },
         deps = {
             ["compat.xext"] = "1.3.7",