When compiled with OpenSSL <= 1.1.1, OpenSSL::SSL::SSLContext#setup
does not raise an exception on an error return from
SSL_CTX_load_verify_locations(), but instead only prints a verbose-mode
warning. This is not helpful since it very likely indicates an actual
error, such as the specified file not being readable.

Also, OpenSSL's error queue is not correctly cleared:

	$ ruby -w -ropenssl -e'OpenSSL.debug=true; ctx=OpenSSL::SSL::SSLContext.new; ctx.ca_file="bad-path"; ctx.setup; pp OpenSSL.errors'
	-e:1: warning: can't set verify locations
	["error:02001002:system library:fopen:No such file or directory",
	 "error:2006D080:BIO routines:BIO_new_file:no such file",
	 "error:0B084002:x509 certificate routines:X509_load_cert_crl_file: system lib"]

The behavior is currently different when compiled with OpenSSL >= 3.0:
SSLError is raised if SSL_CTX_load_verify_file() or
SSL_CTX_load_verify_dir() fails.

This inconsistency was unintentionally introduced by commit https://github.com/ruby/openssl/commit/5375a55ffc35
("ssl: use SSL_CTX_load_verify_{file,dir}() if available", 2020-02-22).
However, raising SSLError seems more appropriate in this situation.
Let's adjust the OpenSSL <= 1.1.1 code so that it behaves the same way
as the OpenSSL >= 3.0 code currently does.

Fixes: https://github.com/ruby/openssl/issues/649

https://github.com/ruby/openssl/commit/7eb10f7b75