The RTS wants a fast, thread-local variable called 'gct'.  However, it turns out
that this is only needed for the parallel garbage collector.

This could be done properly using a register variable (as is done on other
architectures), but - since the iPhone doesn't use the new multi-core ARM chips
yet - it's far safer/easier just to disable the thread-local capability, and
avoid the problem by forcing the GC never to run in parallel.

main() renamed to Haskell_main() just because it's convenient to be able to
write our own start-up routine in C.  This is not necessary at all, and it works
perfectly fine without this change.

--- ghc-6.10.2.orig/rts/sm/GCThread.h	2009-03-31 06:13:16.000000000 +1300
+++ ghc-6.10.2/rts/sm/GCThread.h	2009-06-18 15:54:37.000000000 +1200
@@ -215,6 +215,13 @@
 GLOBAL_REG_DECL(gc_thread*, gct, REG_R1)
 #define DECLARE_GCT /* nothing */
 
+#elif defined(darwin_HOST_OS)
+
+/* iPhone: This is not thread-local, but we also change the code elsewhere
+ * to forbid multi-threaded garbage collection. */
+extern gc_thread* gct;
+#define DECLARE_GCT gc_thread* gct;
+
 #elif defined(__GNUC__)
 
 extern __thread gc_thread* gct;
--- ghc-6.10.2.orig/rts/sm/GC.c	2009-03-31 06:13:16.000000000 +1300
+++ ghc-6.10.2/rts/sm/GC.c	2009-06-18 15:54:37.000000000 +1200
@@ -245,6 +245,7 @@
   /* How many threads will be participating in this GC?
    * We don't try to parallelise minor GC, or mark/compact/sweep GC.
    */
+#if 0
 #if defined(THREADED_RTS)
   if (n < (4*1024*1024 / BLOCK_SIZE) || oldest_gen->steps[0].mark) {
       n_gc_threads = 1;
@@ -254,6 +255,10 @@
 #else
   n_gc_threads = 1;
 #endif
+#else
+  n_gc_threads = 1;  /* iPhone: We must not allow more than one thread, because
+                        'gct' is not thread-local. */
+#endif
   trace(TRACE_gc|DEBUG_gc, "GC (gen %d): %d KB to collect, %ld MB in use, using %d thread(s)",
         N, n * (BLOCK_SIZE / 1024), mblocks_allocated, n_gc_threads);
 
--- ghc-6.10.2.orig/rts/Main.c	2009-03-31 06:13:15.000000000 +1300
+++ ghc-6.10.2/rts/Main.c	2009-06-18 15:54:37.000000000 +1200
@@ -143,7 +143,7 @@
     }
     shutdownHaskellAndExit(exit_status);
 }
-int main(int argc, char *argv[])
+int Haskell_main(int argc, char *argv[])
 {
     /* We do this dance with argc and argv as otherwise the SEH exception
        stuff (the BEGIN/END CATCH below) on Windows gets confused */