[Asm] Add debug tracing in table-generated assembly matcher

This adds debug tracing to the table-generated assembly instruction matcher,
enabled by the -debug-only=asm-matcher option.

The changes in the target AsmParsers are to add an MCInstrInfo reference under
a consistent name, so that we can use it from table-generated code. This was
already being used this way for targets that use deprecation warnings, but 5
targets did not have it, and Hexagon had it under a different name to the other
backends.

llvm-svn: 315445
diff --git a/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp b/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
index 112af62..22ad3cb 100644
--- a/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
+++ b/llvm/lib/Target/X86/AsmParser/X86AsmParser.cpp
@@ -68,7 +68,6 @@
 };
 
 class X86AsmParser : public MCTargetAsmParser {
-  const MCInstrInfo &MII;
   ParseInstructionInfo *InstInfo;
   std::unique_ptr<X86AsmInstrumentation> Instrumentation;
   bool Code16GCC;
@@ -923,7 +922,7 @@
 
   X86AsmParser(const MCSubtargetInfo &sti, MCAsmParser &Parser,
                const MCInstrInfo &mii, const MCTargetOptions &Options)
-      : MCTargetAsmParser(Options, sti), MII(mii), InstInfo(nullptr),
+      : MCTargetAsmParser(Options, sti, mii),  InstInfo(nullptr),
         Code16GCC(false) {
 
     // Initialize the set of available features.