PKCS7 streaming with encode/sign

[JacobBarthelmeh]

ZD16812

[JacobBarthelmeh]

Examples added here wolfSSL/wolfssl-examples#422

[JacobBarthelmeh]

retest this please Jenkins

[douzzer]

Looks good. This is a nice addition!

I left a couple inline comments, and there's also this:

-Wconversion warnings (associated configure options at end, to let you reproduce):

[allcryptonly-Wconversion-intelasm-build] [14 of 30] [5b060453a4]
    configure...   real 0m11.097s  user 0m3.682s  sys 0m8.661s
    build...wolfcrypt/src/asn.c: In function ‘StreamOctetString’:
5b8f3c32d2 (<jacob@wolfssl.com> 2024-01-29 10:45:55 -0700 3495)         if ((sz + i) > inSz) {
wolfcrypt/src/asn.c:3495:17: error: conversion to ‘word32’ {aka ‘unsigned int’} from ‘int’ may change the sign of the result [-Werror=sign-conversion]
 3495 |         if ((sz + i) > inSz) {
      |                 ^
5b8f3c32d2 (<jacob@wolfssl.com> 2024-01-29 10:45:55 -0700 3496)             sz = inSz - i;
wolfcrypt/src/asn.c:3496:18: error: conversion to ‘int’ from ‘word32’ {aka ‘unsigned int’} may change the sign of the result [-Werror=sign-conversion]
 3496 |             sz = inSz - i;
      |                  ^~~~
5b8f3c32d2 (<jacob@wolfssl.com> 2024-01-29 10:45:55 -0700 3499)         ret = SetOctetString(sz, tmp);
wolfcrypt/src/asn.c:3499:30: error: conversion to ‘word32’ {aka ‘unsigned int’} from ‘int’ may change the sign of the result [-Werror=sign-conversion]
 3499 |         ret = SetOctetString(sz, tmp);
      |                              ^~
5b8f3c32d2 (<jacob@wolfssl.com> 2024-01-29 10:45:55 -0700 3499)         ret = SetOctetString(sz, tmp);
wolfcrypt/src/asn.c:3499:15: error: conversion to ‘int’ from ‘word32’ {aka ‘unsigned int’} may change the sign of the result [-Werror=sign-conversion]
 3499 |         ret = SetOctetString(sz, tmp);
      |               ^~~~~~~~~~~~~~
5b8f3c32d2 (<jacob@wolfssl.com> 2024-01-29 10:45:55 -0700 3501)             outIdx += ret;
wolfcrypt/src/asn.c:3501:20: error: conversion to ‘word32’ {aka ‘unsigned int’} from ‘int’ may change the sign of the result [-Werror=sign-conversion]
 3501 |             outIdx += ret;
      |                    ^~
5b8f3c32d2 (<jacob@wolfssl.com> 2024-01-29 10:45:55 -0700 3505)             if (ret + sz + i + outIdx > *outSz) {
wolfcrypt/src/asn.c:3505:26: error: conversion to ‘word32’ {aka ‘unsigned int’} from ‘int’ may change the sign of the result [-Werror=sign-conversion]
 3505 |             if (ret + sz + i + outIdx > *outSz) {
      |                          ^
In file included from ./wolfssl/wolfcrypt/error-crypt.h:34,
                 from wolfcrypt/src/asn.c:105:
85a8c06062 (<douzzer@wolfssl.com> 2021-10-18 23:45:02 -0500 681)             #define XMEMCPY(d,s,l)    memcpy((d),(s),(l))
./wolfssl/wolfcrypt/types.h:681:54: error: conversion to ‘size_t’ {aka ‘long unsigned int’} from ‘int’ may change the sign of the result [-Werror=sign-conversion]
  681 |             #define XMEMCPY(d,s,l)    memcpy((d),(s),(l))
      |                                                      ^~~
5b8f3c32d2 (<jacob@wolfssl.com> 2024-01-29 10:45:55 -0700 3508)             XMEMCPY(tmp + ret, in + i, sz);
wolfcrypt/src/asn.c:3508:13: note: in expansion of macro ‘XMEMCPY’
 3508 |             XMEMCPY(tmp + ret, in + i, sz);
      |             ^~~~~~~
5b8f3c32d2 (<jacob@wolfssl.com> 2024-01-29 10:45:55 -0700 3511)         outIdx += sz;
wolfcrypt/src/asn.c:3511:16: error: conversion to ‘word32’ {aka ‘unsigned int’} from ‘int’ may change the sign of the result [-Werror=sign-conversion]
 3511 |         outIdx += sz;
      |                ^~
5b8f3c32d2 (<jacob@wolfssl.com> 2024-01-29 10:45:55 -0700 3512)         i      += sz;
wolfcrypt/src/asn.c:3512:16: error: conversion to ‘word32’ {aka ‘unsigned int’} from ‘int’ may change the sign of the result [-Werror=sign-conversion]
 3512 |         i      += sz;
      |                ^~
cc1: all warnings being treated as errors
make[2]: *** [Makefile:6873: wolfcrypt/src/src_libwolfssl_la-asn.lo] Error 1
make[1]: *** [Makefile:8036: all-recursive] Error 1
make: *** [Makefile:4754: all] Error 2
   real 0m3.010s  user 0m21.057s  sys 0m3.805s
    allcryptonly-Wconversion-intelasm-build fail_build
    failed config: '--enable-intelasm' '--enable-sp-math-all' '--disable-inline' '--enable-cryptonly' '--enable-all-crypto' '--disable-pwdbased' '--disable-enckeys' '--disable-scrypt' '--disable-camellia' '--disable-md2' '--disable-pkcs7' '--disable-curve25519' '--disable-ed25519' '--disable-ed25519-stream' '--disable-curve448' '--disable-ed448' '--disable-ed448-stream' '--disable-examples' '--disable-benchmark' '--disable-crypttests' 'CC=gcc' 'CPPFLAGS=-Wconversion'

Notice --disable-pkcs7 is in the option list. @dgarske and I never got pkcs7 cleaned up for -Wconversion, so these warnings are just around the new code in asn.c, which isn't gated on HAVE_PKCS7.

[douzzer]

LGTM. tested with super-quick-check.