orc_riscv_target_get_cpu_flags is Linux-specific, rename it and only call it
on Linux.

Implement orc_riscv_target_flush_cache on OpenBSD + clang/compiler-rt.

Fix orc_riscv_target_get_default_flags: the V extension can't be assumed.
On the other hand, on OpenBSD the C extension can be assumed.

Index: orc/riscv/orcriscvtarget.c
--- orc/riscv/orcriscvtarget.c.orig
+++ orc/riscv/orcriscvtarget.c
@@ -69,7 +69,7 @@ orc_riscv_target_detect_extension (const char *exts, c
 }
 
 static orc_uint32
-orc_riscv_target_get_cpu_flags (void)
+orc_riscv_target_get_cpu_flags_linux (void)
 {
   orc_uint32 ret = 0;
 
@@ -114,29 +114,29 @@ orc_riscv_target_get_cpu_flags (void)
 static void
 orc_riscv_target_flush_cache (OrcCode *code)
 {
-#if defined(HAVE_RISCV) && defined(__linux__)
-#if __has_builtin(__builtin___clear_cache)
+#if defined(HAVE_RISCV)
+#if __has_builtin(__builtin___clear_cache) /* compiler-specific */
   __builtin___clear_cache ((char*)code->code, (char*)code->code + code->code_size);
   if ((void *) code->exec != (void *) code->code)
     __builtin___clear_cache ((char*)code->exec, (char*)code->exec + code->code_size);
-#else
+#elif defined(__linux__) /* __clear_cache not really Linux-specific */
   __clear_cache (code->code, code->code + code->code_size);
   if ((void *) code->exec != (void *) code->code)
     __clear_cache (code->exec, code->exec + code->code_size);
-#endif // __builtin___clear_cache
 #else
   ORC_ERROR ("Couldn't flush icache");
   ORC_ASSERT (0);
 #endif
+#endif /* HAVE_RISCV */
 }
 
 static orc_uint32
 orc_riscv_target_get_default_flags (void)
 {
 #if defined(HAVE_RISCV) && defined(__linux__)
-  return orc_riscv_target_get_cpu_flags ();
+  return orc_riscv_target_get_cpu_flags_linux ();
 #else
-  return ORC_TARGET_RISCV_64BIT | ORC_TARGET_RISCV_V;
+  return ORC_TARGET_RISCV_64BIT | ORC_TARGET_RISCV_C;
 #endif
 }
 
@@ -162,8 +162,8 @@ static OrcTarget orc_riscv_target = {
 OrcTarget *
 orc_riscv_target_init (void)
 {
-#ifdef HAVE_RISCV
-  if (orc_riscv_target_get_cpu_flags () & ORC_TARGET_RISCV_V) {
+#if defined(HAVE_RISCV) && defined(__linux__)
+  if (orc_riscv_target_get_cpu_flags_linux () & ORC_TARGET_RISCV_V) {
     ORC_INFO ("This RISC-V CPU supports RVV");
   }
 #endif
