Replace some assert(0)'s with llvm_unreachable.

llvm-svn: 211141
diff --git a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp
index 5c86189..ba95366 100644
--- a/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp
+++ b/llvm/lib/Target/AArch64/MCTargetDesc/AArch64MachObjectWriter.cpp
@@ -75,7 +75,7 @@
     Log2Size = llvm::Log2_32(4);
     switch (Sym->getKind()) {
     default:
-      assert(0 && "Unexpected symbol reference variant kind!");
+      llvm_unreachable("Unexpected symbol reference variant kind!");
     case MCSymbolRefExpr::VK_PAGEOFF:
       RelocType = unsigned(MachO::ARM64_RELOC_PAGEOFF12);
       return true;