add preprocessor option to force crypto lib used by lighttpd base
  -DFORCE_OPENSSL_CRYPTO for OpenSSL
  or -DFORCE_GNUTLS_CRYPTO for GnuTLS
in addition to the already-existing
  -DFORCE_MBEDTLS_CRYPTO for mbed TLS
  or -DFORCE_WOLFSSL_CRYPTO for WolfSSL

This allows building lighttpd with support for multiple TLS modules,
and at the same time specifying the lighttpd base crypto lib dependency.

(Packages such as OpenWRT lighttpd package would need to update
package dependency along with specifying the preprocessor define)

If lighttpd is built with meson and without "-Dwith_nettle=true",
then lighttpd will use mbed TLS if built with "-Dwith_mbedtls",
so the preprocessor option is not strictly necessary for mbed TLS.
However, if built with "-Dwith_mbedtls" and "-Dwith_wolfssl" *and*
without "-Dwith_nettle=true" *and* lighttpd base crypto dependency
on WolfSSL is desired, then CFLAGS -DFORCE_WOLFSSL_CRYPTO is needed,
e.g. with a patch to add it to 'defs' near the top of src/meson.build.
The defines -DFORCE_OPENSSL_CRYPTO or -DFORCE_GNUTLS_CRYPTO are similar
to -DFORCE_WOLFSSL_CRYPTO in that they must be specified to have the
desired effect.

If any -DFORCE_*_CRYPTO is defined, then lighttpd will not use Nettle
and *should not* be built with "-Dwith_nettle=true", in order to avoid
an unnecessary link dependency (though also handled in meson.build).

x-ref:
  "lighttpd authentication modules depends on libnettle"
  openwrt/packages#18851
  "lighttpd: fix missing support for OpenSSL crypto library"
  openwrt/packages#24004

Currently, it is not feasible to configure lighttpd to use OpenSSL as
its internal crypto library. Instead, one must rely on alternative
crypto libraries such as Nettle or mbedTLS. This setup is not ideal in
scenarios where a single crypto library is preferred. To address this
issue, lets propose introducing OpenSSL as an additional configuration
option.  Similarly, propose GnuTLS as additional configuration option.

Closes: openwrt#24004
Co-developed-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>

Currently, it is not feasible to configure lighttpd to use OpenSSL as
its internal crypto library. Instead, one must rely on alternative
crypto libraries such as Nettle or mbedTLS. This setup is not ideal in
scenarios where a single crypto library is preferred. To address this
issue, lets propose introducing OpenSSL as an additional configuration
option.  Similarly, propose GnuTLS as additional configuration option.

Closes: openwrt#24004
Co-developed-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>

Currently, it is not feasible to configure lighttpd to use OpenSSL as
its internal crypto library. Instead, one must rely on alternative
crypto libraries such as Nettle or mbedTLS. This setup is not ideal in
scenarios where a single crypto library is preferred. To address this
issue, lets propose introducing OpenSSL as an additional configuration
option.  Similarly, propose GnuTLS as additional configuration option.

Closes: openwrt#24004
Co-developed-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>

Currently, it is not feasible to configure lighttpd to use OpenSSL as
its internal crypto library. Instead, one must rely on alternative
crypto libraries such as Nettle or mbedTLS. This setup is not ideal in
scenarios where a single crypto library is preferred. To address this
issue, lets propose introducing OpenSSL as an additional configuration
option.  Similarly, propose GnuTLS as additional configuration option.

Closes: openwrt#24004
Co-developed-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>

Currently, it is not feasible to configure lighttpd to use OpenSSL as
its internal crypto library. Instead, one must rely on alternative
crypto libraries such as Nettle or mbedTLS. This setup is not ideal in
scenarios where a single crypto library is preferred. To address this
issue, lets propose introducing OpenSSL as an additional configuration
option.  Similarly, propose GnuTLS as additional configuration option.

Closes: openwrt#24004
Co-developed-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>

Currently, it is not feasible to configure lighttpd to use OpenSSL as
its internal crypto library. Instead, one must rely on alternative
crypto libraries such as Nettle or mbedTLS. This setup is not ideal in
scenarios where a single crypto library is preferred. To address this
issue, lets propose introducing OpenSSL as an additional configuration
option.  Similarly, propose GnuTLS as additional configuration option.

Details of patch:

Each TLS module in lighttpd is built to utilize its corresponding TLS
library. For example, lighttpd's mod_openssl module utilizes OpenSSL,
and its mod_mbedtls module uses mbedTLS.

Separately, the core lighttpd application may employ cryptographic
functions. For efficiency and portability, if lighttpd is compiled with
Nettle, it becomes the default cryptographic library for the base
application. However, each TLS module within lighttpd still relies on
its respective TLS library.

In scenarios where lighttpd is configured with only one TLS library and
without Nettle, the base application adopts the cryptographic functions
from that specific TLS library.

When preparing for Linux distributions, lighttpd might be built with
several TLS modules, where each module uses its designated TLS library.
Presently, lighttpd does not offer a distinct, dedicated option to
select the cryptographic library for the base application.

In contexts like embedded systems, where a single TLS library might be
utilized across the entire base system, specific configurations allow
the use of either mbedTLS or wolfSSL. For these, lighttpd is compiled
with -DFORCE_MBEDTLS_CRYPTO or -DFORCE_WOLFSSL_CRYPTO, respectively.

To extend this capability, let's introduce the FORCE_OPENSSL_CRYPTO
define, enabling lighttpd to also use OpenSSL as an additional
cryptographic library, akin to the existing support for mbedTLS and
wolfSSL.

Closes: openwrt#24004
Co-developed-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>

Currently, it is not feasible to configure lighttpd to use OpenSSL as
its internal crypto library. Instead, one must rely on alternative
crypto libraries such as Nettle or mbedTLS. This setup is not ideal in
scenarios where a single crypto library is preferred. To address this
issue, lets propose introducing OpenSSL as an additional configuration
option.  Similarly, propose GnuTLS as additional configuration option.

Closes: openwrt#24004
Co-developed-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Glenn Strauss <gstrauss@gluelogic.com>
Signed-off-by: Petr Štetiar <ynezz@true.cz>