[Mono-dev] unbreak build on OpenBSD/amd64

[Robert Nagy]

Hey

No UCONTEXT_GREGS on OpenBSD.

Index: mono/mini/exceptions-amd64.c
===================================================================
--- mono/mini/exceptions-amd64.c        (revision 157293)
+++ mono/mini/exceptions-amd64.c        (working copy)
@@ -686,7 +686,7 @@
 gboolean
 mono_arch_handle_exception (void *sigctx, gpointer obj, gboolean test_only)
 {
-#if defined(MONO_ARCH_USE_SIGACTION)
+#if defined(MONO_ARCH_USE_SIGACTION) && defined(UCONTEXT_GREGS)
        /*
         * Handling the exception in the signal handler is problematic, since the original
         * signal is disabled, and we could run arbitrary code though the debugger. So