[build] Avoid use of unportable grep -q

[Jason Merrill]

On 05/10/2010 08:46 AM, Rainer Orth wrote:
> During a recent build on Solaris 8 and 9 with only the native tools, I
> noticed that a couple of uses of grep -q have crept in, which is
> unportable according to the Autoconf manual, and not supported by
> Solaris /usr/bin/grep.
>
> The following patch fixes some of them.  The remaining uses are in
> config.guess (which would have to be fixed upstream first, but only
> affects NetBSD, HP-UX and Linux) and config/tcl.m4, which is probably
> unused at least in the GCC side of the tree, so I've left them alone.
>
> Ok for mainline, 4.5 and 4.4 branches?

I think you probably want to use >/dev/null 2>&1 to redirect stderr as 
well.  OK with that change.

Jason