[JIT/Memory] Fix up semantic of setExecutable().

setExecutable() should do everything that's needed to make the memory
executable on host, i.e. unconditionally set permissions + invalidate
instruction cache. llvm-rtdyld will be updated in my next commit.

Discusseed with: Lang Hames (as part of D13631).

llvm-svn: 253341
diff --git a/llvm/lib/Support/Unix/Memory.inc b/llvm/lib/Support/Unix/Memory.inc
index 4c66b8a..7bffdf3 100644
--- a/llvm/lib/Support/Unix/Memory.inc
+++ b/llvm/lib/Support/Unix/Memory.inc
@@ -264,15 +264,12 @@
 }
 
 bool Memory::setExecutable (MemoryBlock &M, std::string *ErrMsg) {
-#if defined(__APPLE__) && (defined(__arm__) || defined(__arm64__))
   if (M.Address == 0 || M.Size == 0) return false;
   Memory::InvalidateInstructionCache(M.Address, M.Size);
+#if defined(__APPLE__) && (defined(__arm__) || defined(__arm64__))
   kern_return_t kr = vm_protect(mach_task_self(), (vm_address_t)M.Address,
     (vm_size_t)M.Size, 0, VM_PROT_READ | VM_PROT_EXECUTE | VM_PROT_COPY);
   return KERN_SUCCESS == kr;
-#elif defined(__arm__) || defined(__aarch64__)
-  Memory::InvalidateInstructionCache(M.Address, M.Size);
-  return true;
 #else
   return true;
 #endif