c++: Add empty module.cc

This adds an empty module.cc file, along with make rules to build it.

	gcc/cp/
	* module.cc: New dummy file.
	* Make-lang.in: Add rules to build module.o

gcc/cp/Make-lang.in

@@ -54,6 +54,9 @@ c++.serial = cc1plus$(exeext)
 
 CFLAGS-cp/g++spec.o += $(DRIVER_DEFINES)
 
+CFLAGS-cp/module.o += -DHOST_MACHINE=\"$(host)\" \
+	-DTARGET_MACHINE=\"$(target)\"
+
 # Create the compiler driver for g++.
 GXX_OBJS = $(GCC_OBJS) cp/g++spec.o
 xg++$(exeext): $(GXX_OBJS) $(EXTRA_GCC_OBJS) libcommon-target.a $(LIBDEPS)
@@ -81,7 +84,7 @@ CXX_AND_OBJCXX_OBJS = \
 	cp/error.o cp/except.o cp/expr.o \
 	cp/friend.o cp/init.o \
 	cp/lambda.o cp/lex.o cp/logic.o \
-	cp/mangle.o cp/method.o \
+	cp/mangle.o cp/method.o cp/module.o \
 	cp/name-lookup.o cp/optimize.o \
 	cp/parser.o cp/pt.o cp/ptree.o \
 	cp/rtti.o \

gcc/cp/module.cc

@@ -0,0 +1,21 @@
+/* C++ modules.  Experimental!
+   Copyright (C) 2017-2020 Free Software Foundation, Inc.
+   Written by Nathan Sidwell <nathan@acm.org> while at FaceBook
+
+   This file is part of GCC.
+
+   GCC is free software; you can redistribute it and/or modify it
+   under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3, or (at your option)
+   any later version.
+
+   GCC is distributed in the hope that it will be useful, but
+   WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with GCC; see the file COPYING3.  If not see
+<http://www.gnu.org/licenses/>.  */
+
+/* This file intentionally left empty.  */