extconf.rb - fixup to detect openssl info in Ruby build

[MSP-Greg]

Description

A common problem with gems that link to OpenSSL is determining which OpenSSL to use if the system has more than one version installed. One can use --with-openssl-dir, but we'd like to not require its use if possible.

MRI Ruby may contain info in its RbConfig::CONFIG['configure_args'] string that we can use to determine where OpenSSL is. Also, TruffleRuby often embeds the OpenSSL source.

What often happens is that the code in extconf.rb finds the openssl.pc file, but it is for the wrong OpenSSL version.

Update extconf.rb to take the above into account.

Note that --with-openssl-dir is still available, which overrides everything.

Closes #3266. Also see #2790, etc

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