Ok this is trick. avoffset.c includes getfp.c at the end.

clang is used to compile avoffset.c and getfp1.c.
gcc is used to compile getfp.c.

diff -uN inc.orig/avoffset.c inc/avoffset.c
--- inc.orig/avoffset.c	2004-05-09 13:06:08.000000000 +0200
+++ inc/avoffset.c	2009-10-20 16:00:54.000000000 +0200
@@ -36,6 +36,7 @@
 #include <schily.h>
 #include <stdxlib.h>
 #include <signal.h>
+#include <getfp.h>
 
 #ifdef	HAVE_SCANSTACK
 #	include <stkframe.h>
@@ -154,5 +155,3 @@
 	}
 }
 
-#define	IS_AVOFFSET
-#include <getfp.c>
diff -uN inc.orig/getfp.c inc/getfp.c
--- inc.orig/getfp.c	2003-07-13 01:10:47.000000000 +0200
+++ inc/getfp.c	2009-10-20 16:30:36.005762000 +0200
@@ -24,6 +24,8 @@
 #include <standard.h>
 #include <schily.h>
 
+#define IS_AVOFFSET
+
 #ifndef	IS_AVOFFSET
 /*
  * We usually don't like to compile a getfp() that returns junk data in case
@@ -54,45 +56,14 @@
 #	define	FP_OFF		0
 #endif
 
-EXPORT	void	**___fpoff	__PR((char *cp));
+extern	void	**___fpoff	__PR((char *cp));
 
 EXPORT void **
 getfp()
 {
 		long	**dummy[1];
 
-#ifdef	sparc
-	flush_reg_windows(MAXWINDOWS-2);
-#endif
 	return ((void **)((struct frame *)___fpoff((char *)&dummy[0]))->fr_savfp);
 }
 
-/*
- * Don't make it static to avoid inline optimization.
- *
- * We need this function to fool GCCs check for returning addresses
- * from outside the functions local address space.
- */
-EXPORT void **
-___fpoff(cp)
-	char	*cp;
-{
-	long ***lp;
-
-	lp = (long ***)(cp + FP_OFF);
-	lp++;
-	return ((void **)lp);
-}
-
-#ifdef	sparc
-EXPORT int
-flush_reg_windows(n)
-	int	n;
-{
-	if (--n > 0)
-		flush_reg_windows(n);
-	return (0);
-}
-#endif
-
 #endif	/* HAVE_SCANSTACK */
diff -uN inc.orig/getfp.h inc/getfp.h
--- inc.orig/getfp.h	1970-01-01 01:00:00.000000000 +0100
+++ inc/getfp.h	2009-10-20 16:30:36.005762000 +0200
@@ -0,0 +1,5 @@
+EXPORT	void	**___fpoff	__PR((char *cp));
+
+EXPORT void **	getfp();
+
+EXPORT void ** ___fpoff(char *cp);
diff -uN inc.orig/getfp1.c inc/getfp1.c
--- inc.orig/getfp1.c	1970-01-01 01:00:00.000000000 +0100
+++ inc/getfp1.c	2009-10-20 16:30:36.005762000 +0200
@@ -0,0 +1,20 @@
+#include <mconfig.h>
+#include <standard.h>
+#include <schily.h>
+
+#	define	FP_OFF		0
+
+EXPORT	void	**___fpoff	__PR((char *cp));
+
+EXPORT void **
+___fpoff(cp)
+	char	*cp;
+{
+	long ***lp;
+
+	lp = (long ***)(cp + FP_OFF);
+	lp++;
+	return ((void **)lp);
+}
+
+