tools: replace @xxx@ markers at build time

Use the apply-build-vars make macro to replace the @xxx@ markers in
most *.in files only at build time.

As some of the markers are local to tools/configure, introduce
config/Tools-paths.mk.in and add the related make variables to it.
Add Tools-paths to the PATH_FILES make variable in order to include
the definitions for replacing them in the *.in files.

Add the generated files to the distclean target.

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

.gitignore

@@ -47,6 +47,7 @@ config.status
 config.cache
 config/Toplevel.mk
 config/Paths.mk
+config/Tools-paths.mk
 
 dist/*
 extras/