If the build environment does not provide waltham, the agl-compositor fail to build.

In case waltham is not present the build system seems to detected it

Dependency waltham found: NO (tried pkgconfig and cmake)
Message: Waltham requires waltham which was not found.

However, build/config.h includes

#define HAVE_WALTHAM 1

Addtionally, if #define HAVE_WALTHAM 1 is not included the build fails with

{{../src/shell.c: In function ‘ivi_destroy_waltham_destroy’:
../src/shell.c:121:6: error: dereferencing pointer to incomplete type ‘const struct weston_transmitter_api’
api->surface_destroy(surface->waltham_surface.transmitter_surface);
^~
}}