BoringSSL doesn't keep a version number, and doesn't self-identify itself
via any other revision number via its own headers. We can identify
BoringSSL revisions by their commit hash. This hash is typically known by
the builder. This patch adds a way to pass this hash to libcurl, so that
it can display in the curl version string:
For example:
`CFLAGS=-DCURL_BORINGSSL_VERSION="c239ffd0"`
```
curl 7.84.0 (x86_64-w64-mingw32) libcurl/7.84.0 BoringSSL/c239ffd0 (Schannel) zlib/1.2.12 [...]
Release-Date: 2022-06-27
Protocols: dict file ftp ftps gopher gophers http https imap imaps ldap ldaps mqtt pop3 [...]
Features: alt-svc AsynchDNS brotli gsasl HSTS HTTP2 HTTP3 HTTPS-proxy IDN IPv6 Kerberos [...]
```
The setting is optional, and if not passed, BoringSSL will appear without
a version number, like before this patch.
Closes#9113
9153ba708b