Fix get_defconfig_filename() $srctree search order

Previously, $srctree/path/to/defconfig would be looked up before
/path/to/defconfig, and the code wouldn't check if /path/to/defconfig
was an absolute path ($srctree is ignored otherwise). Sloppy old
oversights. The behavior now fully matches the C implementation.

Also fix some related things:

 - An 'if m' suffices to select a defconfig. We previously required 'y'.

 - Make the code less hacky and possibly more Windows-friendly by using
   os.path.relpath() to de-absolutize paths, and stop using
   os.path.normpath() as it could change the meaning of paths that
   contain symbolic links.

 - Explain what happens if 'option defconfig_list' is set on multiple
   symbols and print a warning in that case.

 - Fix get_srctree(). It would previously return "." instead of None if
   $srctree was unset at parse time. Somehow forgot to to test this. The
   code is now much more straightforward.

1 files changed, 0 insertions, 0 deletions

diff --git a/tests/sub/defconfig_in_sub b/tests/sub/defconfig_in_sub
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/tests/sub/defconfig_in_sub