Fix compilation of array subexps.
Fix compilation of array subexps.

mrakgr/futhark,mrakgr/futhark,ihc/futhark,diku-dk/futhark,CulpaBS/wbBach,diku-dk/futhark,ihc/futhark,diku-dk/futhark,HIPERFIT/futhark,HIPERFIT/futhark,diku-dk/futhark,mrakgr/futhark,diku-dk/futhark,HIPERFIT/futhark,ihc/futhark