Frank Benkstein authored Nov 09, 2018 and Brad King committed Nov 13, 2018

Represent the input file path internally in canonical form.  Otherwise
multiple `configure_file` calls that share the same input file but specify
it relative to different directories (e.g. via `../`) result in multiple
copies of the dependency on the rule to re-run CMake.  This causes the
Ninja generator to emit duplicate phony build statements for these
dependencies, which generates an error with `-w dupbuild=err`, which
will be default in Ninja 1.9.

Also canonicalize the output path for consistency.

Add a test case.

Fixes: #18584