I checked out and installed X.org CVS (6.8.99.900) version. X won't start
because:

1. the startx script contains a non POSIX-compliant arithmetic evaluation
2. the installed xprint init script uses arrays, which aren't present in
 strictly POSIX-compliant shells

My /bin/sh is dash.

The first problem can be solved by a trivial patch:

--- programs/xinit/startx.cpp.orig      2005-07-26 01:19:06.000000000 +0200
+++ programs/xinit/startx.cpp   2005-09-14 11:27:09.000000000 +0200
@@ -183,7 +183,7 @@
 EOF
        removelist="$displayname $removelist"
     else
-        dummy=$((dummy+1));
+        dummy=$(($dummy+1));
         xauth -q -f $xserverauthfile << EOF
 add :$dummy . $authcookie
 EOF

The second problem can be solved by specifying /bin/bash instead of
/bin/sh - however this assumes that bash is installed into the /bin
directory which might be false on non-Linux platforms.