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, 1 insertions, 8 deletions

diff --git a/Rakefile b/Rakefile
index 5c5a6e8eb..036894592 100644
--- a/Rakefile
+++ b/Rakefile
@@ -14,14 +14,7 @@ require "mruby-core-ext"
 require "mruby/build"
 
 # load configuration file
-if ENV['MRUBY_CONFIG']
-  MRUBY_CONFIG = ENV['MRUBY_CONFIG']
-  MRUBY_TARGET = File.basename(MRUBY_CONFIG, ".rb")
-else
-  MRUBY_TARGET = ENV['MRUBY_TARGET'] || ENV['TARGET'] || "host"
-  MRUBY_CONFIG = "#{MRUBY_ROOT}/target/#{MRUBY_TARGET}.rb"
-end
-load MRUBY_CONFIG
+MRUBY_CONFIG = MRuby::Build.load_config
 
 # load basic rules
 MRuby.each_target do |build|