mysterious bug: runtime.acid wasn't getting rebuilt

when switching architectures.

fix bug twice: make sure clean removes the file,
and generate into architecture-specific file names.

R=r
http://go/go-review/1013018

src/pkg/runtime/Makefile

@@ -82,9 +82,9 @@ include $(GOROOT)/src/Make.pkg
 clean: clean-local
 
 clean-local:
-	rm -f cgo2c */asm.h
+	rm -f cgo2c */asm.h runtime.acid.*
 
-$(GOARCH)/asm.h: mkasmh.sh runtime.acid
+$(GOARCH)/asm.h: mkasmh.sh runtime.acid.$(GOARCH)
 	./mkasmh.sh >$@.x
 	mv -f $@.x $@
 
@@ -111,5 +111,5 @@ cgo2c: cgo2c.c
 	$(AS) $<
 
 # for discovering offsets inside structs when debugging
-runtime.acid: runtime.h proc.c
-	$(CC) -a proc.c >runtime.acid
+runtime.acid.$(GOARCH): runtime.h proc.c
+	$(CC) -a proc.c >$@

src/pkg/runtime/mkasmh.sh

@@ -55,5 +55,5 @@ aggr != "" && /^	/ {
 	offset=$(NF-1);
 	printf("#define %s_%s %s\n", aggr, name, offset);
 }
-' runtime.acid
+' runtime.acid.$GOARCH