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, 13 insertions, 0 deletions

diff --git a/build_config/host-cxx.rb b/build_config/host-cxx.rb
new file mode 100644
index 000000000..ae05e63c2
--- /dev/null
+++ b/build_config/host-cxx.rb
@@ -0,0 +1,13 @@
+MRuby::Build.new do |conf|
+  toolchain :gcc
+
+  enable_debug
+  # include the default GEMs
+  conf.gembox 'full-core'
+
+  # C compiler settings
+  conf.cc.defines = %w(MRB_ENABLE_DEBUG_HOOK)
+  conf.enable_debug
+  conf.enable_cxx_abi
+  conf.enable_test
+end