source_group: Fix TREE without FILES

According to the documentation of `source_group()` the `FILES`
parameter is optional, but that was actually not the case.
When using `source_group(TREE ${CMAKE_CURRENT_SOURCE_DIR})`
cmake did not previously create the source tree, but recognized
it as the old syntax.  With this patch, cmake recognizes it as
`TREE` syntax if the first argument is TREE followed by a directory.
Then, if no files are given, it defaults to all files in the
directory. PREFIX works too.

Fixes: #24590

0 files changed, 0 insertions, 0 deletions