libtool.m4 usage of diff when comparing files

[Alfred M. Szmidt]

Instead of using diff, we can use cmp which more common than diff.
Reason is that I encountered a (custom) system without diff installed,
but with gcc, and had ./configure output that it could not run diff.

2010-04-24  Alfred M. Szmidt  <address@hidden>

        * libltdl/m4/libtool.m4: Use cmp instead of diff.

--- libltdl/m4/libtool.m4.~1~   2009-11-16 14:11:59.000000000 +0100
+++ libltdl/m4/libtool.m4       2010-04-24 19:29:23.235097505 +0200
@@ -1426,7 +1426,7 @@
      # So say no if there are warnings other than the usual output.
      $ECHO "X$_lt_compiler_boilerplate" | $Xsed -e '/^$/d' >conftest.exp
      $SED '/^$/d; /^ *+/d' conftest.err >conftest.er2
-     if test ! -s conftest.er2 || diff conftest.exp conftest.er2 >/dev/null; 
then
+     if test ! -s conftest.er2 || cmp conftest.exp conftest.er2 >/dev/null; 
then
        $2=yes
      fi
    fi