Dynamically set Homebrew-installed OpenSSL flag

[olivierlacan]

This is a follow-up to #1135 which added the OpenSSL flag assuming that
if the RUBY_PLATFORM is darwin (macOS):

• Homebrew is installed
• OpenSSL is installed via Homebrew

This PR:

• no longer assumes Homebrew is installed if we're on macOS
• no longer assumes OpenSSL is installed via Homebrew
• asks Homebrew for the openssl location (which will also work with the
  newer openssl@1.1 recipe)

Should prevent issues like these when running bundle install on the
rails codebase:

Bundle Install error due to: ld: warning: directory not found for option '-L/usr/local/opt/openssl/lib'

Gem::Ext::BuildError: ERROR: Failed to build gem native extension.
current directory: /Users/olivierlacan/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/bundler/gems/mysql2-7f4e844fccf6/ext/mysql2

/Users/olivierlacan/.rbenv/versions/3.0.1/bin/ruby -I /Users/olivierlacan/.rbenv/versions/3.0.1/lib/ruby/site_ruby/3.0.0 -r ./siteconf20210816-60984-ogpmsf.rb extconf.rb

checking for rb_absint_size()... yes

checking for rb_absint_singlebit_p()... yes

checking for rb_wait_for_single_fd()... yes

checking for rb_enc_interned_str() in ruby.h... yes
Using mysql_config at /opt/homebrew/bin/mysql_config
checking for mysql.h... yes

checking for errmsg.h... yes

checking for SSL_MODE_DISABLED in mysql.h... yes

checking for SSL_MODE_PREFERRED in mysql.h... yes

checking for SSL_MODE_REQUIRED in mysql.h... yes

checking for SSL_MODE_VERIFY_CA in mysql.h... yes

checking for SSL_MODE_VERIFY_IDENTITY in mysql.h... yes

checking for MYSQL.net.vio in mysql.h... yes

checking for MYSQL.net.pvio in mysql.h... no

checking for MYSQL_ENABLE_CLEARTEXT_PLUGIN in mysql.h... yes

checking for SERVER_QUERY_NO_GOOD_INDEX_USED in mysql.h... yes

checking for SERVER_QUERY_NO_INDEX_USED in mysql.h... yes

checking for SERVER_QUERY_WAS_SLOW in mysql.h... yes

checking for MYSQL_OPTION_MULTI_STATEMENTS_ON in mysql.h... yes

checking for MYSQL_OPTION_MULTI_STATEMENTS_OFF in mysql.h... yes

checking for my_bool in mysql.h... no
Don't know how to set rpath on your system, if MySQL libraries are not in path mysql2 may not load

Setting libpath to /opt/homebrew/Cellar/mysql/8.0.26/lib
creating Makefile
current directory: /Users/olivierlacan/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/bundler/gems/mysql2-7f4e844fccf6/ext/mysql2

make DESTDIR= clean
current directory: /Users/olivierlacan/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/bundler/gems/mysql2-7f4e844fccf6/ext/mysql2

make DESTDIR=

compiling client.c

compiling infile.c

compiling mysql2_ext.c

compiling result.c

result.c:259:55: warning: format specifies type 'long' but the argument has type 'int' [-Wformat]

rb_field_type = rb_sprintf("decimal(%ld,%d)", precision, field->decimals);

~~~       ^~~~~~~~~

%d

result.c:258:35: warning: implicit conversion loses integer precision: 'unsigned long' to 'int' [-Wshorten-64-to-32]

precision = field->length - (field->decimals > 0 ? 2 : 1);

~ ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

2 warnings generated.

compiling statement.c

linking shared-object mysql2/mysql2.bundle

ld: warning: directory not found for option '-L/usr/local/opt/openssl/lib'

ld: library not found for -lzstd

clang-12: error: linker command failed with exit code 1 (use -v to see invocation)

make: *** [mysql2.bundle] Error 1
make failed, exit code 2
Gem files will remain installed in /Users/olivierlacan/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/bundler/gems/mysql2-7f4e844fccf6 for inspection.

Results logged to /Users/olivierlacan/.rbenv/versions/3.0.1/lib/ruby/gems/3.0.0/bundler/gems/extensions/arm64-darwin-20/3.0.0/mysql2-7f4e844fccf6/gem_make.out
An error occurred while installing mysql2 (0.5.3), and Bundler cannot continue.

[sodabrew]

The test failures are all due to changes in the performance schema, there's separate work to improve on that.

[ngyl88]

List of issues that should also resolved with this merge:

• ld: library not found for -lssl after Mac OS Sierra upgrade #795
• Gem native extension build fails after upgrade to MacOS 10.4 Mojave #1005
• Library not loaded: libssl.1.1.dylib #1098
• ruby require "mysql2" error #1119
• Library not loaded: libssl.1.1.dylib #1128
• An error occurred while installing mysql2 (0.5.3), and Bundler cannot continue. #1145

Thanks!