Move the logic to test bundled gems to Ruby code

* Writing shell scripts in a Makefile is very error-prone.
* TEST_BUNDLED_GEMS_ALLOW_FAILURES seemed to not work before.

template/Makefile.in

@@ -536,15 +536,7 @@ cont.$(OBJEXT): $(COROUTINE_H)
 TEST_BUNDLED_GEMS_ALLOW_FAILURES =
 
 test-bundled-gems-run:
-	$(Q) fail=0 keep=; case "$(MFLAGS)" in *k*) keep=1;; esac; \
-	while read gem _; do \
-	  echo testing $$gem gem; \
-	  [ $$keep ] || echo $(TEST_BUNDLED_GEMS_ALLOW_FAILURES) | grep -q $$gem || set -e; \
-	  $(XRUBY) -C $(srcdir)/gems/src/$$gem -Ilib ../../../.bundle/bin/rake; \
-	  [ $$? = 0 ] || fail=1; \
-	  set +e; \
-	done < $(srcdir)/gems/bundled_gems; \
-	exit $$fail
+	$(Q) $(XRUBY) $(srcdir)/tool/test-bundled-gems.rb
 
 update-src::
 	@$(CHDIR) "$(srcdir)" && LC_TIME=C exec $(VCSUP)

tool/test-bundled-gems.rb

@@ -0,0 +1,26 @@
+require 'rbconfig'
+
+allowed_failures = ENV['TEST_BUNDLED_GEMS_ALLOW_FAILURES'] || ''
+allowed_failures = allowed_failures.split(',').reject(&:empty?)
+
+exit_code = 0
+File.foreach('gems/bundled_gems') do |line|
+  gem = line.split.first
+  puts "\nTesting the #{gem} gem"
+
+  gem_src_dir = File.expand_path("../../gems/src/#{gem}", __FILE__ )
+  test_command = "#{RbConfig.ruby} -C #{gem_src_dir} -Ilib ../../../.bundle/bin/rake"
+  puts test_command
+  system test_command
+
+  unless $?.success?
+    puts "Tests failed with exit code #{$?.exitstatus}"
+    if allowed_failures.include?(gem)
+      puts "Ignoring test failures for #{gem} due to \$TEST_BUNDLED_GEMS_ALLOW_FAILURES"
+    else
+      exit_code = $?.exitstatus
+    end
+  end
+end
+
+exit exit_code