fix devel/tbb on aarch64

This is enough to get tbb to build and test successfully on aarch64.


Index: patches/patch-build_OpenBSD_inc
===================================================================
RCS file: patches/patch-build_OpenBSD_inc
diff -N patches/patch-build_OpenBSD_inc
--- /dev/null 1 Jan 1970 00:00:00 -0000
+++ patches/patch-build_OpenBSD_inc 29 Dec 2018 18:18:06 -0000
@@ -0,0 +1,15 @@
+$OpenBSD$
+
+Index: build/OpenBSD.inc
+--- build/OpenBSD.inc.orig
++++ build/OpenBSD.inc
+@@ -24,6 +24,9 @@ ifndef arch
+ ifeq ($(shell uname -m),amd64)
+ export arch:=intel64
+ endif
++ ifeq ($(shell uname -m),arm64)
++ export arch:=aarch64
++ endif
+ endif
+
+ ifndef runtime