build: add make.bash --no-clean option

Makes it possible to run

GOARCH=amd64 make.bash
GOARCH=386 make.bash --no-clean

to avoid deleting some of the work done by the first one.

R=golang-dev
CC=golang-dev
https://golang.org/cl/5673056

src/cmd/dist/build.c

@@ -314,12 +314,12 @@ setup(void)
 	p = bpathf(&b, "%s/pkg/%s_%s", goroot, gohostos, gohostarch);
 	if(rebuildall)
 		xremoveall(p);
-	xmkdir(p);
+	xmkdirall(p);
 	if(!streq(goos, gohostos) || !streq(goarch, gohostarch)) {
 		p = bpathf(&b, "%s/pkg/%s_%s", goroot, goos, goarch);
 		if(rebuildall)
 			xremoveall(p);
-		xmkdir(p);
+		xmkdirall(p);
 	}
 	
 	// Create object directory.
@@ -337,7 +337,8 @@ setup(void)
 
 	// Create tool directory.
 	// We keep it in pkg/, just like the object directory above.
-	xremoveall(tooldir);
+	if(rebuildall)
+		xremoveall(tooldir);
 	xmkdirall(tooldir);
 
 	// Remove tool binaries from before the tool/gohostos_gohostarch
@@ -1330,7 +1331,8 @@ cmdbootstrap(int argc, char **argv)
 	if(argc > 0)
 		usage();
 
-	clean();
+	if(rebuildall)
+		clean();
 	goversion = findgoversion();
 	setup();
 	

src/make.bash

@@ -75,8 +75,12 @@ if [ "$1" = "--dist-tool" ]; then
 fi
 
 echo "# Building compilers and Go bootstrap tool for host, $GOHOSTOS/$GOHOSTARCH."
-./cmd/dist/dist bootstrap -a -v # builds go_bootstrap
-# Delay move of dist tool to now, because bootstrap cleared tool directory.
+buildall="-a"
+if [ "$1" = "--no-clean" ]; then
+	buildall=""
+fi
+./cmd/dist/dist bootstrap $buildall -v # builds go_bootstrap
+# Delay move of dist tool to now, because bootstrap may clear tool directory.
 mv cmd/dist/dist $GOTOOLDIR/dist
 $GOTOOLDIR/go_bootstrap clean -i std
 echo