The build system decides whether Legacy3D is available by filtering the
Legacy3D sources per platform and emitting HAVE_LEGACY3D (or USE_LEGACY3D
for RENDERER=legacy) from the result. Key the header include on those
defines instead of re-deriving availability from ANDROID/CORE_GLES, so
GLES targets that keep the renderer see the declaration that
InitRenderers() uses. New ports then only need to touch the source
filter.