add -fno-strict-aliasing to the gcc compiler flags. this is needed, see:

http://www.exim.org/mail-archives/exim-users/Week-of-Mon-20030721/msg00141.html

| It's not a compiler bug.  It is a C99 bug, or more exactly, a
| feature.  C99 changed the semantic of the C language with respect to
| aliasing questions.   Now, the compiler can assume that pointer to
| different types points to different memory location.  This breaks all
| the OO code written in C.
|
| This is a very good idea that the compiler issues a warning message
| because the semantic of language really changed and you want to revert
| to the old semantic.
|
| The make package MUST add -fno-strict-aliasing.  It is not a
| convenience to get rid off warnings.

m4/openbox.m4

@@ -64,7 +64,7 @@ AC_DEFUN([OB_COMPILER_FLAGS],
     if test "$GCC" = "yes"; then
 	AC_MSG_RESULT([yes])
 	if test "$DEBUG" = "yes"; then
-	    FLAGS="$FLAGS -g -fno-inline"
+	    FLAGS="$FLAGS -g -fno-inline -fno-strict-aliasing"
 	    FLAGS="$FLAGS -Wall -Wsign-compare -Waggregate-return"
 	    FLAGS="$FLAGS -Wcast-qual -Wbad-function-cast -Wpointer-arith"
             # for Python.h