Pass $(CROSS_COMPILE) or host GNU type through to upstream build rules.
debian/rules.real: Filter tools packages by host arch, not build arch
debian/rules.d/Makefile: Build the tools needed for headers_install in
a separate subdirectory
* Rename the make macro from submake to make-tools
* Rename debian/stamps/build to debian/stamps/build-tools
* Build them all under debian/build/build-tools/
Add installdir variable that defaults to $(prefix)/$(OUTDIR) as used
in scripts/, but can be set directly in tools/hv which doesn't want
to mirror the source hierarchy.
By passing both -C and -f options to make, we can separate makefiles
from the output directory without adding prefixes to all targets.
We can also reduce the 'clean' commands to little more than 'rm -rf'.
Ben Hutchings