[fortran,patch] Fix LEADZ/TRAILZ

[Tobias Burnus]

Dear FX,

FX wrote:
> The current implementation of LEADZ/TRAILZ has the following bugs:
[...]
> Bootstrapped and regtested on x86_64-linux, comes with testcases.
> OK to commit?

OK. Thanks for finding and fixing this bug.

Tobias

PS: Sorry for initially missing that you fixed the compile-time
simplification with patch.

PPS: Please ignore my previous two emails - a mailserver was not
working for a while; now it does again and it had send all the
spooled emails. In case of gfortran, the patches were meanwhile
already approved and have been checked in.