Fail the build if we encounter an unrecognized command line variable
Fail the build if we encounter an unrecognized command line variable

Fixes #506

dachziegel/thrust,arnabgho/thrust,egaburov/thrust,xiongzhanblake/thrust,mohamed-ali/thrust,xiongzhanblake/thrust,thvasilo/thrust,thvasilo/thrust,GrimDerp/thrust,thrust/thrust,dachziegel/thrust,sarvex/thrust,Ricardo666666/thrust,mohamed-ali/thrust,sdalton1/thrust,jaredhoberock/thrust,zhenglaizhang/thrust,raygit/thrust,andrewcorrigan/thrust-multi-permutation-iterator,mohamed-ali/thrust,egaburov/thrust,arnabgho/thrust,sdalton1/thrust,thrust/thrust,xiongzhanblake/thrust_src,thvasilo/thrust,jaredhoberock/thrust,jaredhoberock/thrust,zeryx/thrust,zeryx/thrust,arnabgho/thrust,thrust/thrust,thrust/thrust,sdalton1/thrust,thrust/thrust,Ricardo666666/thrust,andrewcorrigan/thrust-multi-permutation-iterator,zeryx/thrust,raygit/thrust,xiongzhanblake/thrust,andrewcorrigan/thrust-multi-permutation-iterator,sarvex/thrust,raygit/thrust,egaburov/thrust,jaredhoberock/thrust,sarvex/thrust,marksantos/thrust,zhenglaizhang/thrust,GrimDerp/thrust,zhenglaizhang/thrust,marksantos/thrust,Ricardo666666/thrust,xiongzhanblake/thrust_src,dachziegel/thrust,marksantos/thrust,GrimDerp/thrust,jaredhoberock/thrust,xiongzhanblake/thrust_src