build: build with baseruby that is compiled from the same source

The system installed Ruby (especially Debian) can override
`Gem.default_dir` to lookup gems installed by the OS package managers.
And `rbinstall.rb` respects `Gem.default_dir` to select install
directory of gems under `DESTDIR`. So it installs gems in
`DESTDIR/var/lib/gems/3.2.0+1` where the Debian's `operating_system.rb`
specifies.
However, `Gem.default_dir` is not overridden at runtime on Wasm, so it
lookups `DESTDIR/usr/local/lib/ruby/gems/3.2.0+1` instead. The mismatch
of `default_dir` between install-time and runtime causes the failure of
gem lookup.
To fix this mismatch, stop using system packaged ruby to avoid loading
`operating_system.rb`, and use self-built ruby, which doesn't patch
`Gem.default_dir`.
This change also makes our build compatible with cross-compilation
prerequisite:
https://bugs.ruby-lang.org/projects/ruby/wiki/DeveloperHowto#prerequisite

Author: kateinoigakukun

Rakefile

@@ -105,9 +105,17 @@ class BuildPlan
     "#{ext_build_dir}/extinit.o"
   end
 
+  def baseruby_name
+    "baseruby-#{@params[:src]}"
+  end
+
+  def baseruby_path
+    "#{@base_dir}/build/deps/#{RbConfig::CONFIG["host"]}/opt/#{baseruby_name}/bin/ruby"
+  end
+
   def dep_tasks
-    return [] if @params[:profile] == "minimal"
-    ["deps:libyaml-#{@params[:target]}"]
+    return [baseruby_name] if @params[:profile] == "minimal"
+    [baseruby_name, "deps:libyaml-#{@params[:target]}"]
   end
 
   def check_deps
@@ -149,6 +157,7 @@ class BuildPlan
     args << "--with-static-linked-ext"
     args << %Q(--with-ext="#{default_exts}")
     args << %Q(--with-libyaml-dir="#{deps_install_dir}/libyaml/usr/local")
+    args << %Q(--with-baseruby="#{baseruby_path}")
 
     case target
     when "wasm32-unknown-wasi"
@@ -226,6 +235,18 @@ namespace :build do
     file source.configure_file => [source.src_dir] do
       sh "./autogen.sh", chdir: source.src_dir
     end
+
+    baseruby_install_dir = File.join(Dir.pwd, "/build/deps/#{RbConfig::CONFIG["host"]}/opt/baseruby-#{name}")
+    baseruby_build_dir   = File.join(Dir.pwd, "/build/deps/#{RbConfig::CONFIG["host"]}/baseruby-#{name}")
+
+    directory baseruby_build_dir
+
+    desc "build baseruby #{name}"
+    task "baseruby-#{name}" => [source.src_dir, source.configure_file, baseruby_build_dir] do
+      next if Dir.exist?(baseruby_install_dir)
+      sh "#{source.configure_file} --prefix=#{baseruby_install_dir} --disable-install-doc", chdir: baseruby_build_dir
+      sh "make install", chdir: baseruby_build_dir
+    end
   end
 
   BUILDS.each do |params|

builders/wasm32-unknown-emscripten/Dockerfile

@@ -2,7 +2,7 @@ FROM emscripten/emsdk:2.0.13
 
 RUN set -eux; \
   apt-get update; \
-  apt-get install ruby bison make autoconf git curl -y; \
+  apt-get install ruby bison make autoconf git curl build-essential libyaml-dev -y; \
   curl -fsSL https://deb.nodesource.com/setup_16.x | bash -; \
   apt-get install nodejs -y; \
   apt-get clean; \

builders/wasm32-unknown-wasi/Dockerfile

@@ -17,7 +17,7 @@ ENV WASI_SDK_PATH="/opt/wasi-sdk"
 
 RUN set -eux; \
   apt-get update; \
-  apt-get install ruby bison make autoconf git curl -y; \
+  apt-get install ruby bison make autoconf git curl build-essential libyaml-dev -y; \
   curl -fsSL https://deb.nodesource.com/setup_16.x | bash -; \
   apt-get install nodejs -y; \
   apt-get clean; \