Give it a chance to build on ppc & mips

Index: src/greenlet/slp_platformselect.h
--- src/greenlet/slp_platformselect.h.orig
+++ src/greenlet/slp_platformselect.h
@@ -17,9 +17,9 @@ extern "C" {
 # include "platform/switch_amd64_unix.h" /* gcc on amd64 */
 #elif defined(__GNUC__) && defined(__i386__)
 # include "platform/switch_x86_unix.h" /* gcc on X86 */
-#elif defined(__GNUC__) && defined(__powerpc64__) && (defined(__linux__) || defined(__FreeBSD__))
+#elif defined(__GNUC__) && defined(__powerpc64__) && (defined(__linux__) || defined(__FreeBSD__) || defined(__OpenBSD__))
 # include "platform/switch_ppc64_linux.h" /* gcc on PowerPC 64-bit */
-#elif defined(__GNUC__) && defined(__PPC__) && (defined(__linux__) || defined(__FreeBSD__))
+#elif defined(__GNUC__) && defined(__PPC__) && (defined(__linux__) || defined(__FreeBSD__) || defined(__OpenBSD__))
 # include "platform/switch_ppc_linux.h" /* gcc on PowerPC */
 #elif defined(__GNUC__) && defined(__POWERPC__) && defined(__APPLE__)
 # include "platform/switch_ppc_macosx.h" /* Apple MacOS X on 32-bit PowerPC */
@@ -50,7 +50,7 @@ extern "C" {
 # else
 #  include "platform/switch_arm32_gcc.h" /* gcc using arm32 */
 # endif
-#elif defined(__GNUC__) && defined(__mips__) && defined(__linux__)
+#elif defined(__GNUC__) && defined(__mips__) && (defined(__linux__) || defined(__openbsd__))
 # include "platform/switch_mips_unix.h" /* Linux/MIPS */
 #elif defined(__GNUC__) && defined(__aarch64__)
 # include "platform/switch_aarch64_gcc.h" /* Aarch64 ABI */
