[imcc] Fixed last remaining -O2 issue #1044 t/pmc/exception-old_19.pir

Stop constant propagation at yield or invokecc for possible
push_eh/pop_eh non-local effects. This can undo the set of the constant
value.

See t/pmc/exception-old_19.pir:
cont = test() contains a push_eh, and the subsequent pop_eh at cont() changes
the value of the constant redux from 0 back to 1. So constant propagation for
redux=0 cannot delete "if redux goto done" and the done branch.
[cage] add .gdbinit and .lldbinit to .gitignore