[Build] Add rule to generate fully-expanded .td file

I found it useful in the past and now again to have a version of the .td file
where all the records are expanded.  This adds a makefile rule to generate
this on demand.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@208056 91177308-0d34-0410-b5e6-96231b3b80d8

Makefile.rules

@@ -1713,8 +1713,14 @@ $(ObjDir)/%GenDFAPacketizer.inc.tmp : %.td $(ObjDir)/.dir $(LLVM_TBLGEN)
 	$(Echo) "Building $(<F) DFA packetizer tables with tblgen"
 	$(Verb) $(LLVMTableGen) -gen-dfa-packetizer -o $(call SYSPATH, $@) $<
 
+# Dump all the records to <target>.td.expanded.  This is useful for debugging.
+$(TARGET:%=%.td.expanded): \
+%.td.expanded : %.td $(LLVM_TBLGEN)
+	$(Echo) "Building a fully expanded version of $(<F)"
+	$(Verb) $(LLVMTableGen) -o $(call SYSPATH, $@) $<
+
 clean-local::
-	-$(Verb) $(RM) -f $(INCFiles)
+	-$(Verb) $(RM) -f $(INCFiles) $(TARGET).td.expanded
 
 endif # TARGET