teach mklog to look in the current directory for ChangeLog files

 when run in repos other than gcc mklog fails to find ChangeLog files
because it looks for $0/../$dir/ChangeLog, but of course if the diff is
for a project other than gcc that might not exist.  It should be fine to
also look for $cwd/$dir/ChangeLog, and use that if we find it.  This
means that for example in binutils-gdb.git you can do git commit,
and then in your editor read git diff HEAD~ | mklog - to generate a
template ChangeLog for that commit.

contrib/ChangeLog:

2016-03-06  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>

	* mklog: Look for the ChangeLog file in $cwd.

From-SVN: r234014

contrib/ChangeLog

+2016-03-06  Trevor Saunders  <tbsaunde+gcc@tbsaunde.org>
+
+	* mklog: Look for the ChangeLog file in $cwd.
+
 2016-02-26  Joel Sherrill <joel@rtems.org>
 
 	* config-list.mk: Add aarch64-rtems and x86_64-rtems

contrib/mklog

@@ -104,7 +104,7 @@ sub get_clname ($) {
 	my $dirname = $_[0];
 	while ($dirname) {
 		my $clname = "$dirname/ChangeLog";
-		if (-f "$gcc_root/$clname") {
+		if (-f "$gcc_root/$clname" || -f "$clname") {
 			my $relname = substr ($_[0], length ($dirname) + 1);
 			return ($clname, $relname);
 		} else {