Fix libcompiler_rt __clear_cache() on armv7

[Josh Elsasser]

I came across some code which uses __clear_cache() from
libgcc/libcompiler_rt on 32-bit arm. Currently that just falls through
to abort(), but enabling the existing sysarch() code works for me.

diff --git a/lib/libcompiler_rt/clear_cache.c b/lib/libcompiler_rt/clear_cache.c
index 451f1c0b124..4902d761b81 100644
--- a/lib/libcompiler_rt/clear_cache.c
+++ b/lib/libcompiler_rt/clear_cache.c
@@ -33,7 +33,7 @@ uintptr_t GetCurrentProcess(void);
   #include <machine/sysarch.h>
 #endif
 
-#if defined(__OpenBSD__) && defined(__mips__)
+#if defined(__OpenBSD__) && (defined(__mips__) || defined(__arm__))
   #include <sys/types.h>
   #include <machine/sysarch.h>
 #endif
@@ -102,7 +102,7 @@ void __clear_cache(void *start, void *end) {
  * so there is nothing to do
  */
 #elif defined(__arm__) && !defined(__APPLE__)
-    #if defined(__FreeBSD__) || defined(__NetBSD__)
+    #if defined(__FreeBSD__) || defined(__NetBSD__) || defined(__OpenBSD__)
         struct arm_sync_icache_args arg;
 
         arg.addr = (uintptr_t)start;