configure: Add an option to use the cargo build system

This commit adds a `--enable-rustbuild` option to the configure script which
will copy a different `Makefile.in` into place to intercept all `make`
invocations.

Currently this makefile only has one target, but it's expected to be filled out
quite a bit over time!

configure

@@ -606,6 +606,7 @@ opt stage0-landing-pads 1 "enable landing pads during bootstrap with stage0"
 opt dist-host-only 0 "only install bins for the host architecture"
 opt inject-std-version 1 "inject the current compiler version of libstd into programs"
 opt llvm-version-check 1 "check if the LLVM version is supported, build anyway"
+opt rustbuild 0 "use the rust and cargo based build system"
 
 # Optimization and debugging options. These may be overridden by the release channel, etc.
 opt_nosave optimize 1 "build optimized rust code"
@@ -1422,7 +1423,7 @@ done
 step_msg "configuring submodules"
 
 # Have to be in the top of src directory for this
-if [ -z $CFG_DISABLE_MANAGE_SUBMODULES ]
+if [ -z $CFG_DISABLE_MANAGE_SUBMODULES ] && [ -z $CFG_ENABLE_RUSTBUILD ]
 then
     cd ${CFG_SRC_DIR}
 
@@ -1481,7 +1482,11 @@ do
         ;;
     esac
 
-    if [ -z $CFG_LLVM_ROOT ]
+    if [ -n "$CFG_ENABLE_RUSTBUILD" ]
+    then
+        msg "not configuring LLVM, rustbuild in use"
+        do_reconfigure=0
+    elif [ -z $CFG_LLVM_ROOT ]
     then
         LLVM_BUILD_DIR=${CFG_BUILD_DIR}$t/llvm
         if [ -n "$CFG_DISABLE_OPTIMIZE_LLVM" ]
@@ -1812,8 +1817,15 @@ do
     putvar $CFG_LLVM_INST_DIR
 done
 
+if [ -n "$CFG_ENABLE_RUSTBUILD" ]
+then
+    INPUT_MAKEFILE=src/bootstrap/mk/Makefile.in
+else
+    INPUT_MAKEFILE=Makefile.in
+fi
+
 msg
-copy_if_changed ${CFG_SRC_DIR}Makefile.in ./Makefile
+copy_if_changed ${CFG_SRC_DIR}${INPUT_MAKEFILE} ./Makefile
 move_if_changed config.tmp config.mk
 rm -f config.tmp
 touch config.stamp

src/bootstrap/mk/Makefile.in

@@ -0,0 +1,23 @@
+# Copyright 20126 The Rust Project Developers. See the COPYRIGHT
+# file at the top-level directory of this distribution and at
+# http://rust-lang.org/COPYRIGHT.
+#
+# Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+# http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+# <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+# option. This file may not be copied, modified, or distributed
+# except according to those terms.
+
+include config.mk
+include $(CFG_SRC_DIR)mk/util.mk
+
+ifdef VERBOSE
+BOOTSTRAP_ARGS := -v
+else
+BOOTSTRAP_ARGS :=
+endif
+
+BOOTSTRAP := $(CFG_PYTHON) $(CFG_SRC_DIR)src/bootstrap/bootstrap.py $(BOOTSTRAP_ARGS)
+
+all:
+	$(Q)$(BOOTSTRAP)