DebugInfo: Avoid emitting standard opcode lengths in debug_line.dwo headers where opcodes are never used anyway

Introduce a slightly tighter wrapper around the header structure that
handles this use case. (MCDwarfDwoLineTable)

llvm-svn: 204101
diff --git a/llvm/test/DebugInfo/X86/generate-odr-hash.ll b/llvm/test/DebugInfo/X86/generate-odr-hash.ll
index e01863d..9770163 100644
--- a/llvm/test/DebugInfo/X86/generate-odr-hash.ll
+++ b/llvm/test/DebugInfo/X86/generate-odr-hash.ll
@@ -141,6 +141,8 @@
 
 ; CHECK-LABEL: .debug_line.dwo contents:
 ; FISSION: Line table prologue
+; FISSION: opcode_base: 1
+; FISSION-NOT: standard_opcode_lengths
 ; FISSION-NOT: file_names[
 ; FISSION: file_names{{.*}} bar.h
 ; FISSION: file_names{{.*}} bar.cpp