(compile nil '(lambda () (char=))) ; Caught WARNING: ; Wrong number of arguments for CHAR=.

; Compilation unit finished ; Caught 1 WARNING condition

#<FUNCTION (LAMBDA ()) {456E3EB3}> NIL NIL

while it should be T, T.

jvm-compile, which handles this doesn't succeed because the underlying with-compilation-unit eats all the warnings and errors so that jvm-compile's handler-bind doesn't get a piece of them. Binding *resignal-compiler-warnings* to T inside jvm-compile resolves this.