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, 11 insertions, 0 deletions

diff --git a/build_config/android_armeabi.rb b/build_config/android_armeabi.rb
new file mode 100644
index 000000000..41a657c3b
--- /dev/null
+++ b/build_config/android_armeabi.rb
@@ -0,0 +1,11 @@
+# Requires Android NDK r13 or later.
+MRuby::CrossBuild.new('android-armeabi') do |conf|
+  params = {
+    :arch => 'armeabi',
+    :platform => 'android-24',
+    :toolchain => :clang,
+  }
+  toolchain :android, params
+
+  conf.gembox 'default'
+end