Fix configuration error on Solaris

[Bruno Haible]

When building poke on Solaris, already the configuration fails:

...
configure: back from the recursive configuration in jitter
checking for jitter-config... 
/home/haible/poke-0.90/build-x86-64-cc/jitter/bin/jitter-config
configure: WARNING: non-working jitter-config at 
/home/haible/poke-0.90/build-x86-64-cc/jitter/bin/jitter-config
configure: error: could not find jitter-config in Jitter sub-package within

Let's see why:

$ jitter/bin/jitter-config --best-dispatch
grep: illegal option -- q
Usage: grep -hblcnsviw pattern file . . .
jitter/bin/jitter-config: --best-dispatch is a non-option argument.
Try 'jitter/bin/jitter-config --help' for more information.

$ jitter/bin/jitter-config --help         
grep: illegal option -- q
Usage: grep -hblcnsviw pattern file . . .
jitter/bin/jitter-config: --help is a non-option argument.
Try 'jitter/bin/jitter-config --help' for more information.

The use of 'grep -q' is a known portability problem. Citing
<https://www.gnu.org/savannah-checkouts/gnu/autoconf/manual/autoconf-2.70/html_node/Limitations-of-Usual-Tools.html>:
  "Don’t use ‘grep -q’ to suppress output, because many grep
   implementations (e.g., Solaris) do not support -q. ... Instead,
   redirect the standard output and standard error (in case the file
   doesn’t exist) of grep to /dev/null."

Here is a proposed patch.

0004-Fix-configuration-error-on-Solaris.patch
Description: Text Data