Add `big_endian` and `little_endian` methods to `CrossBuild`; ref
When your target machine is big endian, specify as following in the
`build_config.rb`:
```ruby
MRuby::CrossBuild.new('32bit') do |conf|
toolchain :gcc
conf.big_endian
end
```
MODIFY
lib/mruby/build.rb
lib/mruby/build.rb
@@ -334,6 +334,7 @@ EOS
attr_accessor :host_target, :build_target
def initialize(name, build_dir=nil, &block)
+ @endian = nil
@test_runner = Command::CrossTestRunner.new(self)
super
end
@@ -351,5 +352,26 @@ EOS
@test_runner.run(mrbtest)
end
end
+
+ def big_endian
+ if @endian
+ puts "Endian has already specified as #{@endian}."
+ return
+ end
+ @endian = :big
+ @mrbc.compile_options += ' -E'
+ compilers.each do |c|
+ c.defines += %w(MRB_ENDIAN_BIG)
+ end
+ end
+
+ def little_endian
+ if @endian
+ puts "Endian has already specified as #{@endian}."
+ return
+ end
+ @endian = :little
+ @mrbc.compile_options += ' -e'
+ end
end # CrossBuild
end # MRuby

Add `big_endian` and `little_endian` methods to `CrossBuild`; ref #3922

When your target machine is big endian, specify as following in the
`build_config.rb`:

```ruby
MRuby::CrossBuild.new('32bit') do |conf|
  toolchain :gcc

  conf.big_endian
end
```