MC/Mach-O: Fail faster/harder when we see .file, which isn't yet supported.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@104031 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/MC/MCMachOStreamer.cpp b/lib/MC/MCMachOStreamer.cpp
index 629a6ba..f1dc349 100644
--- a/lib/MC/MCMachOStreamer.cpp
+++ b/lib/MC/MCMachOStreamer.cpp
@@ -142,10 +142,10 @@
                                  unsigned char Value = 0);
   
   virtual void EmitFileDirective(StringRef Filename) {
-    errs() << "FIXME: MCMachoStreamer:EmitFileDirective not implemented\n";
+    report_fatal_error("unsupported directive: '.file'");
   }
   virtual void EmitDwarfFileDirective(unsigned FileNo, StringRef Filename) {
-    errs() << "FIXME: MCMachoStreamer:EmitDwarfFileDirective not implemented\n";
+    report_fatal_error("unsupported directive: '.file'");
   }
   
   virtual void EmitInstruction(const MCInst &Inst);