kbuild: Handle external SUBDIRS with modversions

We need to collect a list of all modules during the recursive build. I used
a "touch .tmp_versions/<path/to/module.ko>" to do so, which however doesn't
work so well, when path/to isn't inside the kernel tree.
  
The best way to build external modules is currently using kbuild by saying
"make SUBDIRS=/some/external/dir modules", which was thus broken. While this
way is not all that optimal and I hope to come up with something better
before 2.6, it works and should keep working, so this patch fixes the usage
above.
  
Instead of touching files with the entire path added, we just create a
<module>.mod file in $(MODVERDIR) now, and save the path to the module.ko 
in it. Since module names are unique, a flat hierarchy is actually fine here.

Makefile

@@ -408,6 +408,7 @@ ifdef CONFIG_MODVERSIONS
 ifdef KBUILD_MODULES
 ifeq ($(origin SUBDIRS),file)
 	$(Q)rm -rf $(MODVERDIR)
+	$(Q)mkdir $(MODVERDIR)
 else
 	@echo '*** Warning: Overriding SUBDIRS on the command line can cause'
 	@echo '***          inconsistencies with module symbol versions'

scripts/Makefile.build

@@ -47,7 +47,7 @@ endif
 
 ifdef CONFIG_MODVERSIONS
 modules := $(obj-m)
-touch-module = @mkdir -p $(MODVERDIR)/$(@D); touch $(MODVERDIR)/$(@:.o=.ko)
+touch-module = @echo $(@:.o=.ko) > .tmp_versions/$(@F:.o=.mod)
 else
 modules := $(obj-m:.o=.ko)
 endif

scripts/Makefile.modver

@@ -9,7 +9,7 @@ include scripts/Makefile.lib
 
 #
 
-modules := $(patsubst ./%,%,$(shell cd $(MODVERDIR); find . -name \*.ko))
+modules := $(shell cd $(MODVERDIR); cat *.mod)
 
 __modversions: $(modules)
 	@: