recommend use of gperf version 3

[Bruno Haible]

Hello Ranjit,

>   They should also be tested with Jacks:
>
>   http://gcc.gnu.org/install/test.html#TOC2
>
> There *should not* be any regressions, but you never
> know...
>
> I assume that you bootstrapped and tested for regressions
> after you applied your patch. Were you able to measure any
> improvements in performance?

Sorry, I did not do all this (re-bootstrapping, regression-testing, measuring).
But I know gperf well enough to be confident in the modified command-line
options.

I'm hoping that someone from the GCC developers likes the patch and commits
it for me, and that the performance change may show up in the automatic
builds.

Bruno