In addition, update the documents referring `build_config.rb` which is
no longer used. The new `build_config.rb` describes the new configuration
structure in the comment.
* 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).
There are 3 levels of C++ exception handling:
* default - no C++ exception (use setjmp/longjmp)
* enable_cxx_exception (use C++ exceptions with C ABI)
* enable_cxx_abi (use C++ ABI including exceptions)
ref #3267#3470
By this commit, mruby do not use C++ ABI mode unless
you specify explicitly. It compiles C files by C
compilers, with C++ exception enabled when it sees
C++ files in your configured mrbgems.
I haven't tried visualcpp, so please submit an issue
if you see any problem with C++ gems on Windows.
KOBAYASHI Shuji