I think it might be due to the latest wayland-egl commits... ...but I'm not sure if this is something that Mesa would need to update first... ...or if it's unintentional 
I get this output: 

  CC       drivers/dri2/platform_x11_dri3.lo
drivers/dri2/platform_wayland.c: In function ‘dri2_wl_create_window_surface’:
drivers/dri2/platform_wayland.c:293:21: error: ‘struct wl_egl_window’ has no member named ‘private’
    dri2_surf->wl_win->private = dri2_surf;
                     ^~
drivers/dri2/platform_wayland.c: In function ‘dri2_wl_destroy_surface’:
drivers/dri2/platform_wayland.c:379:24: error: ‘struct wl_egl_window’ has no member named ‘private’
       dri2_surf->wl_win->private = NULL;
                        ^~
Makefile:1153: recipe for target 'drivers/dri2/platform_wayland.lo' failed
make[4]: *** [drivers/dri2/platform_wayland.lo] Error 1
make[4]: *** Waiting for unfinished jobs....
make[4]: Leaving directory '/srcbuild/mesa/src/egl'
Makefile:960: recipe for target 'all' failed
make[3]: *** [all] Error 2
make[3]: Leaving directory '/srcbuild/mesa/src/egl'
Makefile:863: recipe for target 'all-recursive' failed
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory '/srcbuild/mesa/src'
Makefile:654: recipe for target 'all' failed
make[1]: *** [all] Error 2
make[1]: Leaving directory '/srcbuild/mesa/src'
Makefile:667: recipe for target 'all-recursive' failed
make: *** [all-recursive] Error 1
PackageCompileSource finished in 321 seconds