[compiler-rt] Implement __clear_cache() on OpenBSD/mips64

[visa]

Summary

Make __clear_cache() invoke the platform's cache flush function
on OpenBSD/mips64.

[krytarowski]

Do you want me to land it for you?

[visa]

In D42332#982871, @krytarowski wrote:

Do you want me to land it for you?

Yes please.

lib/builtins/clear_cache.c

#if defined(__FreeBSD__) && defined(__arm__)
   #include <sys/types.h>
   #include <machine/sysarch.h>
 #endif
 
 #if defined(__NetBSD__) && defined(__arm__)
   #include <machine/sysarch.h>
 #endif
 
+#if defined(__OpenBSD__) && defined(__mips__)
+  #include <sys/types.h>
+  #include <machine/sysarch.h>
+#endif
+
 #if defined(__linux__) && defined(__mips__)
   #include <sys/cachectl.h>
   #include <sys/syscall.h>
   #include <unistd.h>
   #if defined(__ANDROID__) && defined(__LP64__)
     /*
      * clear_mips_cache - Invalidates instruction cache for Mips.
      */
#if defined(__ANDROID__) && defined(__LP64__)
         if ((end_int - start_int) <= address_range_limit) {
             clear_mips_cache(start, (end_int - start_int));
         } else {
             syscall(__NR_cacheflush, start, (end_int - start_int), BCACHE);
         }
     #else
         syscall(__NR_cacheflush, start, (end_int - start_int), BCACHE);
     #endif
+#elif defined(__mips__) && defined(__OpenBSD__)
+  cacheflush(start, (uintptr_t)end - (uintptr_t)start, BCACHE);
 #elif defined(__aarch64__) && !defined(__APPLE__)
   uint64_t xstart = (uint64_t)(uintptr_t) start;
   uint64_t xend = (uint64_t)(uintptr_t) end;
   uint64_t addr;
 
   // Get Cache Type Info
   uint64_t ctr_el0;
   __asm __volatile("mrs %0, ctr_el0" : "=r"(ctr_el0));