Add androideabi toolchain rake task (Build mruby with Android NDK)

tasks/toolchains/androideabi.rake

@@ -0,0 +1,23 @@
+# Download and unarchive latest Android NDK from https://developer.android.com/tools/sdk/ndk/index.html
+# Make custom standalone toolchain as described here (android_ndk/docs/STANDALONE-TOOLCHAIN.html)
+# Please export custom standalone toolchain path
+#   export ANDROID_STANDALONE_TOOLCHAIN=/tmp/android-14-toolchain
+
+# Add to your build_config.rb
+# MRuby::CrossBuild.new('androideabi') do |conf|
+#   toolchain :androideabi
+# end
+
+MRuby::Toolchain.new(:androideabi) do |conf|
+  toolchain :gcc
+
+  ANDROID_STANDALONE_TOOLCHAIN = ENV['ANDROID_STANDALONE_TOOLCHAIN'] + '/bin/arm-linux-androideabi-'
+  SYSROOT = ENV['ANDROID_STANDALONE_TOOLCHAIN'] + '/sysroot'
+
+  [conf.cc, conf.cxx, conf.objc, conf.asm].each do |cc|
+    cc.command = ENV['CC'] || ANDROID_STANDALONE_TOOLCHAIN + 'gcc'
+    cc.flags = [ENV['CFLAGS'] || ['--sysroot ' + SYSROOT]]
+  end
+  conf.linker.command = ENV['LD'] || ANDROID_STANDALONE_TOOLCHAIN + 'gcc'
+  conf.archiver.command = ENV['AR'] || ANDROID_STANDALONE_TOOLCHAIN + 'ar'
+end