don't know about mandrake but generally
sould be a symbolic link named X11 in
/usr/include
Code:
/usr/include $ ls -l X11
lrwxrwxrwx 1 root root 20 2004-12-25 00:09 X11 -> ../X11R6/include/X11
this would make the include PATH /usr/X11R6/include i think and similar below
and in /usr/lib
Code:
/usr/lib $ ls -l X11
lrwxrwxrwx 1 root root 16 2004-12-25 00:08 X11 -> ../X11R6/lib/X11
and an entry in PKG_CONFIG_PATH /usr/X11R6/lib/pkgconfig