xfwm4 cvs compilation - Xpm lib not found

[ForSpam]

Hi,

Currently I am trying to compile xfce4 from the recent cvs tree.
During the ./configure of xfwm4 I get the following error message:

"checking for main in -lX11... no
checking for main in -lXpm... no
configure: error: The Xpm library was not found on you system"

But the xpm lib. is installed on my slackware 9.1 system.
The stable version (4.0.5) of xfwm4 is working just fine.

I allready searched the mailinglists and forum but didn't find a clue on 
this.  

Best regards
Alexander G.