generated configure script doesn't work when "diff" isn't available

[Vincent Lefevre]

Hi,

The generated configure script doesn't work on platforms where the
"diff" utility isn't available, such as Nokia's N810 Internet tablet
(with Maemo/OS2008, using BusyBox v1.6.1).

In fact, there are two problems:

1. The first test that uses diff fails with an obscure error message.
In my case, in "checking for grep that handles long lines and -e",
I got an error saying that a working grep could not be found. So,
I first thought the problem came from grep, until I remembered that
"diff" wasn't available.

2. The failure itself.

Even though the GNU standards require "diff" to be present, fixing
the problem would be useful in practice, and the fix is easy: use
"cmp" instead of "diff" ("cmp" is available on the N810). I don't
know about the other platforms. So, I'd say that one of the two
commands should be tested, and if it doesn't work, test the other
one. If both fail, then output an error message.

To reproduce the problem, try to build MPFR 2.3.1[*] for instance.
The configure works OK after:

  sed -i -e 's/diff /cmp /' configure

[*] http://www.mpfr.org/mpfr-2.3.1/mpfr-2.3.1.tar.bz2

-- 
Vincent Lefèvre <address@hidden> - Web: <http://www.vinc17.org/>
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Work: CR INRIA - computer arithmetic / Arenaire project (LIP, ENS-Lyon)