gh-114332: Fix the flags reference for re.compile() (#114334)

The GH-93000 change set inadvertently caused a sentence in re.compile()
documentation to refer to details that no longer followed. Correct this
with a link to the Flags sub-subsection.

Co-authored-by: Adam Turner <[email protected]>

Author: dhgutteridge

Doc/library/re.rst

@@ -880,8 +880,8 @@ Functions
    below.
 
    The expression's behaviour can be modified by specifying a *flags* value.
-   Values can be any of the following variables, combined using bitwise OR (the
-   ``|`` operator).
+   Values can be any of the `flags`_ variables, combined using bitwise OR
+   (the ``|`` operator).
 
    The sequence ::