Check the compiler's not all there (5)
I believe the answer is:
barmy
'not all there' is the definition.
(both can informally mean mad)
'check the compiler's' is the wordplay.
'check' becomes 'bar' (bar can mean to restrict or check).
'the compiler's' becomes 'my' (I've seen this in other clues).
'bar'+'my'='BARMY'
(Other definitions for barmy that I've seen before include "Bonkers" , "Mad (slang)" , "round the bend" , "like Basil, arguably?" , "Crackers, daft" .)