meson: dep_libdecor is disabled without wayland
Fixes the build when wayland is not installed.
src/egl/eglut/meson.build:34:0: ERROR: Unknown variable "dep_libdecor".
Fixes the build when wayland is not installed.
src/egl/eglut/meson.build:34:0: ERROR: Unknown variable "dep_libdecor".