Apply thread allocations patch to Ruby 2.7

This makes us to compile Ruby 2.7 manually
and apply relevant patch.

scripts/install-ruby

@@ -1,14 +1,50 @@
 #!/bin/bash
-set -xeuo pipefail
-IFS=$'\n\t'
 
-cd /tmp
-wget http://cache.ruby-lang.org/pub/ruby/2.2/ruby-2.2.2.tar.gz
-tar -xvzf ruby-2.2.2.tar.gz
+set -xeou pipefail
 
-cd ruby-2.2.2
+# Based on https://github.com/docker-library/ruby/blob/master/2.7/buster/Dockerfile
+
+RUBY_VERSION=${1}
+RUBY_MAJOR=${1%.*} # strip last component
+RUBY_DOWNLOAD_SHA256=${2}
+
+RUBY_DOWNLOAD_URL="https://cache.ruby-lang.org/pub/ruby/${RUBY_MAJOR%-rc}/ruby-$RUBY_VERSION.tar.xz"
+
+# Download Ruby
+curl -fsSL "$RUBY_DOWNLOAD_URL" -o ruby.tar.xz
+echo "${RUBY_DOWNLOAD_SHA256} ruby.tar.xz" | sha256sum -c -
+
+# Skip installing Gem docs
+mkdir -p /usr/local/etc
+echo 'install: --no-document' >> /usr/local/etc/gemrc
+echo 'update: --no-document' >> /usr/local/etc/gemrc
+
+# Install needed packages
+apt-get update
+apt-get install -y --no-install-recommends bison dpkg-dev libgdbm-dev ruby
+
+# Unpack Ruby
+mkdir -p /usr/src/ruby
+tar -xJf ruby.tar.xz -C /usr/src/ruby --strip-components=1
+rm ruby.tar.xz
+cd /usr/src/ruby
+
+# Apply patches
+find /patches/ruby/$RUBY_VERSION -name '*.patch' -print0 | xargs -0 -n1 patch -p1 -i
 ./configure --enable-shared --disable-install-doc --disable-install-rdoc --disable-install-capi
-make install -j 3
+make install -j $(nproc)
 
+# Cleanup
 cd /
-rm -rf /tmp/*
+rm -rf /usr/src/ruby
+apt-get purge -y --auto-remove ruby
+
+# Verify
+# verify we have no "ruby" packages installed
+! dpkg -l | grep -i ruby
+[ "$(command -v ruby)" = '/usr/local/bin/ruby' ]
+
+# rough smoke test
+ruby --version
+gem --version
+bundle --version