[SV 62278] Only expand the first pattern during secondary expansion

[SV 62278] Only expand the first pattern during secondary expansion

During normal pattern rule expansion only the first pattern (%) is
expanded; however during secondary expansion all patterns were
expanded.  Modify secondary expansion to match the behavior of normal
expansion.

Implementation tweaked by Paul Smith <psmith@gnu.org>

* src/file.c (expand_deps): Don't use subst_expand() which replaces
all % with $*: instead replace only the first one, by hand.
Fix a memory leak where the dep structure was not always freed.
* tests/scripts/features/statipattrules: Use .RECIPEPREFIX not TAB.
Add a series of tests verifying that static pattern rules with and
without secondary expansion both return the same results.