[MIR] Add support for the frame-destroy MachineInstr flag

We are printing / parsing the `frame-setup` MachineInstr flag but not
the `frame-destroy` one.

Differential Revision: https://reviews.llvm.org/D41509

llvm-svn: 322071
diff --git a/llvm/lib/CodeGen/MIRParser/MILexer.h b/llvm/lib/CodeGen/MIRParser/MILexer.h
index 0204d54..275f929 100644
--- a/llvm/lib/CodeGen/MIRParser/MILexer.h
+++ b/llvm/lib/CodeGen/MIRParser/MILexer.h
@@ -63,6 +63,7 @@
     kw_renamable,
     kw_tied_def,
     kw_frame_setup,
+    kw_frame_destroy,
     kw_debug_location,
     kw_cfi_same_value,
     kw_cfi_offset,