Add generic arch include header

For a newer glibc, this should work (as we don't need private
splice defines, for instance).

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/arch/arch.h b/arch/arch.h
index 9f2a566..0ad7b6e 100644
--- a/arch/arch.h
+++ b/arch/arch.h
@@ -17,6 +17,8 @@
 	arch_sparc,
 	arch_sparc64,
 	arch_arm,
+
+	arch_generic,
 };
 
 #if defined(__i386__)
@@ -40,7 +42,8 @@
 #elif defined(__mips__) || defined(__mips64__)
 #include "arch-mips.h"
 #else
-#error "Unsupported arch"
+#warning "Unknown architecture, attempting to use generic model."
+#include "arch-generic.h"
 #endif
 
 #ifdef ARCH_HAVE_FFZ