file: Sort GLOB results to make it deterministic (#14491)

Even though the `file(GLOB)` documentation specifically warns against
using it to collect a list of source files, projects often do it anyway.
Since it uses `readdir()`, the list of files will be unsorted.
This list is often passed directly to add_executable / add_library.
Linking binaries with an unsorted list will make it unreproducible,
which means that the produced binary will differ depending on the
unpredictable `readdir()` order.

To solve those reproducibility issues in a lot of programs (which don't
explicitly `list(SORT)` the list manually), sort the resulting list of
the `file(GLOB)` command.

A more detailed rationale about reproducible builds is available
[here](https://reproducible-builds.org/).

1 files changed, 3 insertions, 2 deletions

diff --git a/Help/command/file.rst b/Help/command/file.rst
index 96ac6c7..256d16d 100644
--- a/Help/command/file.rst
+++ b/Help/command/file.rst
@@ -103,8 +103,9 @@ Generate a list of files that match the ``<globbing-expressions>`` and
 store it into the ``<variable>``.  Globbing expressions are similar to
 regular expressions, but much simpler.  If ``RELATIVE`` flag is
 specified, the results will be returned as relative paths to the given
-path.  No specific order of results is defined.  If order is important then
-sort the list explicitly (e.g. using the :command:`list(SORT)` command).
+path.  No specific order of results is defined other than that it is
+deterministic.  If order is important then sort the list explicitly
+(e.g. using the :command:`list(SORT)` command).
 
 By default ``GLOB`` lists directories - directories are omited in result if
 ``LIST_DIRECTORIES`` is set to false.