libwebsockets-v4.3-stable: build fails when building with mbedtls

[lukakudra]

When building libwebsockets configured with -DLWS_WITH_SSL=ON and -DLWS_WITH_MBEDTLS=ON from branch v4.3-stable the build fails when mbedtls library is built without MBEDTLS_VERSION_C defined.

The compiler warning is the following:

warning: implicit declaration of function 'mbedtls_version_get_string' [-Wimplicit-function-declaration]
  791 |         mbedtls_version_get_string(mbedtls_version);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~

and this warning results in a linker error:

 undefined reference to `mbedtls_version_get_string'

This issue is present on OpenWrt because the mbedtls library is built without the option MBEDTLS_VERSION_C as you can see here.

The solution to this problem is quite simple because there is actually no need to use the function mbedtls_version_get_string, you can simply use the definition MBEDTLS_VERSION_STRING and the code functionality will remain the same.
In the commit that introduced this issue the following changes need to be made:

1. delete the code between lines 389 and 391
2. delete the code between lines 790 and 792
3. change the line 796 to this: "LWS: %s, MbedTLS-%s %s%s", library_version, MBEDTLS_VERSION_STRING, opts_str, s);

I can also make a pull request with these changes if you would prefer that.

[lws-team]

Thanks, I pushed your change on v4.3-stable and main.