build: introduce if_changed_deps

This macro does compare command line like if_changed, but it also
rewrite the dependencies generated by $(CC) in order to depend on a
CONFIG_* as generated by kconfig instead of depending on autoconf.h.
This allow to make a change in kconfig options and only rebuild the
object that uses that CONFIG_* option.

cmd_and_record isn't needed anymore as it is replace by
cmd_and_fixdep.

There's only one .*.d dependency file left which is explicitly
included as a workound, all the other are been absorb into the .*.cmd
dependency files via `fixdep`. So including .*.d can be removed from
the makefile.

Also adjust "cloc" recipe due to .*.d been replace by .*.cmd files.

This imports fixdep.c and if_changed_deps macro from Linux v5.12.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

.gitignore

@@ -328,6 +328,7 @@ xen/include/xen/lib/x86/cpuid-autogen.h
 xen/test/livepatch/config.h
 xen/test/livepatch/expect_config.h
 xen/test/livepatch/*.livepatch
+xen/tools/fixdep
 xen/tools/kconfig/.tmp_gtkcheck
 xen/tools/kconfig/.tmp_qtcheck
 xen/tools/symbols