meson 0.47.1 is failing if the conditions are on multiple lines:

$ meson -Dnmea-source=false -Dmodem-gps-source=false -Dcdma-source=false -D3g-source=false -Ddemo-agent=false -Dgtk-doc=true build
[...]
src/meson.build:93:3: ERROR:  Unknown statement