With 0.8.28, "machdep_init" seems obsoleted/removed but forgotten to be
cleaned for the arch powerpc, hence FTBFS; commenting the whole code.

Index: uae-0.8.28/src/md-ppc-gcc/support.c
===================================================================
--- uae-0.8.28.orig/src/md-ppc-gcc/support.c	2008-06-26 12:07:50.000000000 +0000
+++ uae-0.8.28/src/md-ppc-gcc/support.c	2008-07-05 12:42:38.000000000 +0000
@@ -20,6 +20,7 @@
 
 void machdep_init (void)
 {
+/*
     rpt_available = 1;
     write_log ("Calibrating delay loop.. ");
     fflush(stderr);
@@ -35,6 +36,7 @@
     write_log ("ok - %d\n",best_time/loops_to_go);
     last_time = read_processor_time();
     best_time = read_processor_time()-last_time;
+*/
 }