Build process updated:

You have to specify `TARGET` to specify a configuration, e.g.

```
rake TARGET=host-debug all test
```

When you port `mruby` to a new configuration:
1. copy an existing configuration under `target` directory
2. modify the new configuration file
3. build using the new configuration
4. send PR if you please

1 files changed, 98 insertions, 0 deletions

diff --git a/target/host.rb b/target/host.rb
new file mode 100644
index 000000000..4f0286882
--- /dev/null
+++ b/target/host.rb
@@ -0,0 +1,98 @@
+MRuby::Build.new do |conf|
+  # load specific toolchain settings
+
+  # Gets set by the VS command prompts.
+  if ENV['VisualStudioVersion'] || ENV['VSINSTALLDIR']
+    toolchain :visualcpp
+  else
+    toolchain :gcc
+  end
+
+  # Use mrbgems
+  # conf.gem 'examples/mrbgems/ruby_extension_example'
+  # conf.gem 'examples/mrbgems/c_extension_example' do |g|
+  #   g.cc.flags << '-g' # append cflags in this gem
+  # end
+  # conf.gem 'examples/mrbgems/c_and_ruby_extension_example'
+  # conf.gem :core => 'mruby-eval'
+  # conf.gem :mgem => 'mruby-onig-regexp'
+  # conf.gem :github => 'mattn/mruby-onig-regexp'
+  # conf.gem :git => '[email protected]:mattn/mruby-onig-regexp.git', :branch => 'master', :options => '-v'
+
+  # include the GEM box
+  conf.gembox 'full-core'
+
+  # C compiler settings
+  # conf.cc do |cc|
+  #   cc.command = ENV['CC'] || 'gcc'
+  #   cc.flags = [ENV['CFLAGS'] || %w()]
+  #   cc.include_paths = ["#{root}/include"]
+  #   cc.defines = %w()
+  #   cc.option_include_path = %q[-I"%s"]
+  #   cc.option_define = '-D%s'
+  #   cc.compile_options = %Q[%{flags} -MMD -o "%{outfile}" -c "%{infile}"]
+  # end
+
+  # mrbc settings
+  # conf.mrbc do |mrbc|
+  #   mrbc.compile_options = "-g -B%{funcname} -o-" # The -g option is required for line numbers
+  # end
+
+  # Linker settings
+  # conf.linker do |linker|
+  #   linker.command = ENV['LD'] || 'gcc'
+  #   linker.flags = [ENV['LDFLAGS'] || []]
+  #   linker.flags_before_libraries = []
+  #   linker.libraries = %w()
+  #   linker.flags_after_libraries = []
+  #   linker.library_paths = []
+  #   linker.option_library = '-l%s'
+  #   linker.option_library_path = '-L%s'
+  #   linker.link_options = "%{flags} -o "%{outfile}" %{objs} %{libs}"
+  # end
+
+  # Archiver settings
+  # conf.archiver do |archiver|
+  #   archiver.command = ENV['AR'] || 'ar'
+  #   archiver.archive_options = 'rs "%{outfile}" %{objs}'
+  # end
+
+  # Parser generator settings
+  # conf.yacc do |yacc|
+  #   yacc.command = ENV['YACC'] || 'bison'
+  #   yacc.compile_options = %q[-o "%{outfile}" "%{infile}"]
+  # end
+
+  # gperf settings
+  # conf.gperf do |gperf|
+  #   gperf.command = 'gperf'
+  #   gperf.compile_options = %q[-L ANSI-C -C -p -j1 -i 1 -g -o -t -N mrb_reserved_word -k"1,3,$" "%{infile}" > "%{outfile}"]
+  # end
+
+  # file extensions
+  # conf.exts do |exts|
+  #   exts.object = '.o'
+  #   exts.executable = '' # '.exe' if Windows
+  #   exts.library = '.a'
+  # end
+
+  # file separetor
+  # conf.file_separator = '/'
+
+  # Turn on `enable_debug` for better debugging
+  # enable_debug
+  enable_debug
+  conf.enable_bintest
+  conf.enable_test
+end
+
+MRuby::Build.new('test') do |conf|
+  # Gets set by the VS command prompts.
+  if ENV['VisualStudioVersion'] || ENV['VSINSTALLDIR']
+    toolchain :visualcpp
+  else
+    toolchain :gcc
+  end
+
+  conf.gembox 'default'
+end