[flang] legacy branch target (#75628)
Branching to an endif statement from outside of the if is nonconformant:
subroutine jump(n)
goto 6
if (n == 3) then
goto 7
6 end if
print *, 'pass'
return
7 print *, 'fail'
end
However, this branch was permitted up to f90. Account for this usage
when rewriting if constructs and if statements by suppressing rewriting
if the end statement is labeled.
