openssl: Stop dragging libpthread into every libcrypto user.

With the new _NETBSD_PTHREAD_CREATE_WEAK, libcrypto can have a call
to pthread_create without linking against libpthread, so it is not
necessary to link all libcrypto users against libpthread too.

Applications that link against libcrypto but not libpthread can't use
threaded OpenSSL functionality, of course -- OSSL_set_max_threads
will always fail in such applications.

This reverts all the makefile churn that I found for unnecessary
libpthread linkage since the openssl 3.5 import.

PR lib/59685: libcrypto should not depend on libpthread

branches: 1.4.2;
crypto needs threads

branches: 1.3.16;
use OPENSSL_API_COMPAT

use OpenSSL-1.1 apis

branches: 1.1.2; 1.1.4;
Add nbsvtool, a simple and small program to create and verify detached
PKCS7 signatures. This was written by lha@ and discussed on
tech-security. I've slightly cleaned up the program and man page.
Contrary to the original version, this doesn't provide a default trust
anchor.

New sentence, new line.

Fix markup

branches: 1.4.2; 1.4.6; 1.4.8;
Remove trailing whitespace. Fix formatting. Remove superfluous .Pp.

Improve with information provided by Joerg.

There are some formatting errors, someone with mandoc clue please correct.

Also, this man page assumes familiarity with the concepts uesd.
While fully describing these concepts is outside the scope of this
man page, a pointer to such a description should be included.
Someone who knows of such a description, please provide pointers.

Finally, we should have a companion tool to create the peaces needed
to use this tool: set up a CA, create a certificate chain and a
private key/certificate pair for signing.

Formatting improvements. Use standard headers and macros.
Fix typos. Bump date for import.

branches: 1.1.2;
Add nbsvtool, a simple and small program to create and verify detached
PKCS7 signatures. This was written by lha@ and discussed on
tech-security. I've slightly cleaned up the program and man page.
Contrary to the original version, this doesn't provide a default trust
anchor.

fix various typos in comments, documentation and messages.

mark old compat functions.

use OpenSSL-1.1 apis

branches: 1.2.2;
If key usage validation is requested, ensure that all bits exist.
Check the certificates before printing that the signature is valid.
Improvide wording of error message as suggested by Love.

branches: 1.1.2;
Add nbsvtool, a simple and small program to create and verify detached
PKCS7 signatures. This was written by lha@ and discussed on
tech-security. I've slightly cleaned up the program and man page.
Contrary to the original version, this doesn't provide a default trust
anchor.