When installing transset on Gentoo (amd64), portage complains about a compiler warning (gcc 4.4.2):

QA Notice: Package has poor programming practices which may compile fine but exhibit random runtime failures.
* transSet.c:68: warning: incompatible implicit declaration of built-in function 'memcpy'

This seems to be resolved easily with an additional include of string.h:

--- a/transSet.c        2009-12-09 22:05:07.000000000 +0100    
+++ b/transSet.c        2009-12-09 22:05:07.000000000 +0100
@@ -13,6 +13,7 @@
 #include <X11/Xatom.h>
 #include "dsimple.h"
 #include <stdlib.h>
+#include <string.h>


 Window target_win;


There is another compiler warning (without Gentoo QA notice) in dsimple.c:

dsimple.c: In function 'Window_With_Name':
dsimple.c:478: warning: comparison between signed and unsigned integer expressions

This one also seems to have a simple fix

--- a/dsimple.c 2009-12-09 22:10:02.000000000 +0100
+++ b/dsimple.c 2009-12-09 22:11:26.000000000 +0100
@@ -464,8 +464,7 @@
      char *name;
 {
        Window *children, dummy;
-       unsigned int nchildren;
-       int i;
+       unsigned int i, nchildren;
        Window w=0;
        char *window_name;