Revert `MRUBY_TARGET` mechanism; ref #5096

* In explanation of mruby, the expression `build_config.rb` is frequently
  used including official documents, so I think that it will not make sense
  if the file is no longer used.
* The `MRUBY_TARGET` mechanism seems to have little improvement, so I don't
  think it should be changed to avoid unnecessary confusion.
* `MRUBY_TARGET` and `MRuby.targets` represent somewhat different things,
  so using the same term "target" is a bit confusing.

The mechanism that can be written short when using a file under
`build_config` (renamed from `target`) directory remains
(`build_config/${MRUBY_CONFIG}.rb` is used if the path specified
in `MRUBY_CONFIG` doesn't exist).

1 files changed, 14 insertions, 0 deletions

diff --git a/build_config/cross-32bit.rb b/build_config/cross-32bit.rb
new file mode 100644
index 000000000..82d5d023f
--- /dev/null
+++ b/build_config/cross-32bit.rb
@@ -0,0 +1,14 @@
+# Define cross build settings
+MRuby::CrossBuild.new('cross-32bit') do |conf|
+  toolchain :gcc
+
+  conf.cc.flags << "-m32"
+  conf.linker.flags << "-m32"
+
+  # conf.build_mrbtest_lib_only
+
+  conf.gem :core => "mruby-bin-mruby"
+  conf.gem "#{MRUBY_ROOT}/examples/mrbgems/c_and_ruby_extension_example"
+
+  conf.test_runner.command = 'env'
+end