Handle ASN1_SET_OF and PKCS12_STACK_OF using function
casts in the same way as STACK_OF.

be needed in some ENGINE code, and might serve elsewhere as well.
Note that it's implemented in such a way that the locking itself is
done through the same CRYPTO_lock function as the static locks.

WARNING: This is currently experimental and untested code (it will get
tested soon, though :-)).

sk_whatever_insert and sk_whatever_set immediately reveals the subtle
difference in parameter order.

Change mkstack.pl so that safestack.h is not rewritten when
nothing has changed.

After some messing around this seems to work but needs
a few more tests. Working out the syntax for sk_set_cmp_func()
(cast it to a function that itself returns a function pointer)
was painful :-(

Needs some testing to see what other compilers think of this
syntax.

Also needs similar stuff for ASN1_SET_OF etc etc.

structures and functions for each stack type. The previous behaviour
can be enabled by configuring with the "-DDEBUG_SAFESTACK" option.
This will also cause "make update" (mkdef.pl in particular) to
update the libeay.num and ssleay.num symbol tables with the number of
extra functions DEBUG_SAFESTACK creates.

The way this change works is to accompany each DECLARE_STACK_OF()
macro with a set of "#define"d versions of the sk_##type##_***
functions that ensures all the existing "type-safe" stack calls are
precompiled into the underlying stack calls. The presence or abscence
of the DEBUG_SAFESTACK symbol controls whether this block of
"#define"s or the DECLARE_STACK_OF() macro is taking effect. The
block of "#define"s is in turn generated and maintained by a perl
script (util/mkstack.pl) that encompasses the block with delimiting
C comments. This works in a similar way to the auto-generated error
codes and, like the other such maintenance utilities, is invoked
by the "make update" target.

A long (but mundane) commit will follow this with the results of
"make update" - this will include all the "#define" blocks for
each DECLARE_STACK_OF() statement, along with stripped down
libeay.num and ssleay.num files.

same one). However, the first will temporarily break things until the
second comes through. :-)

The safestack.h handling was mapping compare callbacks that externally
are of the type (int (*)(type **,type **)) into the underlying callback
type used by stack.[ch], which is (int (*)(void *,void *)). After some
degree of digging, it appears that the callback type in the underlying
stack code should use double pointers too - when the compare operations
are invoked (from sk_find and sk_sort), they are being used by bsearch
and qsort to compare two pointers to pointers. This change corrects the
prototyping (by only casting to the (void*,void*) form at the moment
it is needed by bsearch and qsort) and makes the mapping in safestack.h
more transparent. It also changes from "void*" to "char*" to stay in
keeping with stack.[ch]'s assumed base type of "char".

Also - the "const" situation was that safestack.h was throwing away
"const"s, and to compound the problem - a close examination of stack.c
showed that (const char **) is not really achieving what it is supposed
to when the callback is being invoked, what is needed is
(const char * const *). So the underlying stack.[ch] and the mapping
macros in safestack.h have all been altered to correct this.

What will follow are the vast quantities of "const" corrections required
in stack-dependant code that was being let "slip" through when
safestack.h was discarding "const"s. These now all come up as compiler
warnings.

to minimise the effects on existing code.

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Reviewed by:
PR: