AArch64: Fix asserting on unexpected triples (#147880)

Author: arsenm

llvm/lib/Target/AArch64/MCTargetDesc/AArch64MCTargetDesc.cpp

@@ -356,7 +356,7 @@ static MCAsmInfo *createAArch64MCAsmInfo(const MCRegisterInfo &MRI,
   else if (TheTriple.isOSBinFormatCOFF())
     MAI = new AArch64MCAsmInfoGNUCOFF();
   else
-    llvm_unreachable("Invalid target"); // FIXME: This is not unreachable
+    reportFatalUsageError("unsupported object format");
 
   // Initial state of the frame pointer is SP.
   unsigned Reg = MRI.getDwarfRegNum(AArch64::SP, true);

llvm/test/CodeGen/AArch64/unsupported-object-format-err.ll

@@ -0,0 +1,10 @@
+; RUN: not llc -mtriple=aarch64-pc-unknown-xcoff -filetype=null %s 2>&1 | FileCheck %s
+; RUN: not llc -mtriple=aarch64-pc-unknown-goff -filetype=null %s 2>&1 | FileCheck %s
+
+; Make sure there is no crash or assert with unexpected object
+; formats.
+
+; CHECK: LLVM ERROR: unsupported object format
+define void @foo() {
+  ret void
+}