PATCH: Install four PCH files instead of one

[Benjamin Kosnik]

>Benjamin, this patch replaces a piece of the first patch you posted to
>enable PCH.  Sorry, I just noticed that you made changes (because you
>had to) when you made it respect configure-time checks in the second
>version.

Yeah. Sadly, the patch posted last night redid this completely. I'm
assuming things are mostly working on BSD? Should I just check that in?
I think the fallout will be pretty minimal, but I'd like to get a round
of testing in before Friday and the weekend sets in.

>Although, I'm afraid of installing ~50MB of PCH files, I think
>creating ~four PCH files is better than just one.  This set will cover
>most user options provided (and indeed all situations I found while
>first working with the PCH stuff, running make check from top-level
>vs. within libstdc++-v3, rebuilding from top-level vs. within
>libstdc++-v3): -O0, -O2, "-O0 -g", "-O2 -g".

Hmmm. Had not thought of this. 

I'm in favor of this, and if this needs to be changed/added/subtracted
in the future as experience is gained it'll be easy enough to do. 

>Also, note, please don't touch something in ${glibcpp_srcdir}.
>The whole reason for a stamp file should remove any need to touch it.

Agreed.

I think the stamp file thing in general is a last resort. I redid the
patch to remove this part entirely. The 'touch ${pch_output}' was
assumed to be in the build directory.... if it needs to be explicit
can't you just do touch ${builddir}/${pch_output}?

>(I'll update it and commit it once I see yours go in and you say you
>agree; or else free feel to include it in your before you first commit.)

Let's do it after?

-benjamin