Configure: don't mangle the directory again when checking DEPEND inclusion

When generating the correct inclusion directory for DEPEND, we mangled
it to be relative to the build or the source directory.  However, the
value we handle already come with a correct directory, so we only need
to use it as is.

Fixes #5543

Reviewed-by: Tim Hudson <tjh@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/5546)