Fix compat with RubyInstaller-2.4 on Windows

Since RubyInstaller-2.4+ is bundled with MSYS2 and the libmariadbclient
can be installed per gemspec library dependency, it is easy to build
the mysql2 gem in Windows.

The MSYS2/MINGW dependency feature is documented here:
https://github.com/oneclick/rubyinstaller2/wiki/For-gem-developers#msys2-library-dependency

This also adds ruby-2.4 binaries, so that the mysql2 is still usabel as
a binary gem.

Fixes brianmario#861

Gemfile

@@ -3,7 +3,7 @@ source 'https://rubygems.org'
 gemspec
 
 gem 'rake', '~> 10.4.2'
-gem 'rake-compiler', '~> 0.9.5'
+gem 'rake-compiler', '~> 1.0'
 
 group :test do
   gem 'eventmachine' unless RUBY_PLATFORM =~ /mswin|mingw/
@@ -22,7 +22,7 @@ end
 
 group :development do
   gem 'pry'
-  gem 'rake-compiler-dock', '~> 0.5.1'
+  gem 'rake-compiler-dock', '~> 0.6.0'
 end
 
 platforms :rbx do

appveyor.yml

@@ -25,6 +25,8 @@ test_script:
 #  - find tmp -name "*.log" -exec cat {};
 environment:
   matrix:
+    - ruby_version: "24-x64"
+    - ruby_version: "24"
     - ruby_version: "23-x64"
     - ruby_version: "23"
     - ruby_version: "22-x64"

ext/mysql2/extconf.rb

@@ -177,7 +177,7 @@ def add_ssl_defines(header)
   $CFLAGS << ' -g -fno-omit-frame-pointer'
 end
 
-if RUBY_PLATFORM =~ /mswin|mingw/
+if RUBY_PLATFORM =~ /mswin|mingw/ && !defined?(RubyInstaller)
   # Build libmysql.a interface link library
   require 'rake'
 

lib/mysql2.rb

@@ -13,16 +13,20 @@
     ENV['RUBY_MYSQL2_LIBMYSQL_DLL']
   elsif File.exist?(File.expand_path('../vendor/libmysql.dll', File.dirname(__FILE__)))
     # Use vendor/libmysql.dll if it exists, convert slashes for Win32 LoadLibrary
-    File.expand_path('../vendor/libmysql.dll', File.dirname(__FILE__)).tr('/', '\\')
+    File.expand_path('../vendor/libmysql.dll', File.dirname(__FILE__))
+  elsif defined?(RubyInstaller)
+    # RubyInstaller-2.4+ native build
   else
     # This will use default / system library paths
     'libmysql.dll'
   end
 
-  require 'Win32API'
-  LoadLibrary = Win32API.new('Kernel32', 'LoadLibrary', ['P'], 'I')
-  if 0 == LoadLibrary.call(dll_path)
-    abort "Failed to load libmysql.dll from #{dll_path}"
+  if dll_path
+    require 'Win32API'
+    LoadLibrary = Win32API.new('Kernel32', 'LoadLibrary', ['P'], 'I')
+    if 0 == LoadLibrary.call(dll_path)
+      abort "Failed to load libmysql.dll from #{dll_path}"
+    end
   end
 end
 

mysql2.gemspec

@@ -13,4 +13,6 @@ Mysql2::GEMSPEC = Gem::Specification.new do |s|
 
   s.files = `git ls-files README.md CHANGELOG.md LICENSE ext lib support`.split
   s.test_files = `git ls-files spec examples`.split
+
+  s.metadata['msys2_mingw_dependencies'] = 'libmariadbclient'
 end

tasks/compile.rake

@@ -9,7 +9,7 @@ Rake::ExtensionTask.new("mysql2", Mysql2::GEMSPEC) do |ext|
   # clean compiled extension
   CLEAN.include "#{ext.lib_dir}/*.#{RbConfig::CONFIG['DLEXT']}"
 
-  if RUBY_PLATFORM =~ /mswin|mingw/
+  if RUBY_PLATFORM =~ /mswin|mingw/ && !defined?(RubyInstaller)
     # Expand the path because the build dir is 3-4 levels deep in tmp/platform/version/
     connector_dir = File.expand_path("../../vendor/#{vendor_mysql_dir}", __FILE__)
     ext.config_options = ["--with-mysql-dir=#{connector_dir}"]
@@ -77,7 +77,7 @@ task :devkit do
 end
 
 if RUBY_PLATFORM =~ /mingw|mswin/
-  Rake::Task['compile'].prerequisites.unshift 'vendor:mysql'
+  Rake::Task['compile'].prerequisites.unshift 'vendor:mysql' unless defined?(RubyInstaller)
   Rake::Task['compile'].prerequisites.unshift 'devkit'
 else
   if Rake::Task.tasks.map(&:name).include? 'cross'