Ruby » Ruby master

r57401 introduced parallel ext configuration, which has broken make install when configuring Ruby using the --with-static-linked-ext option. Specifically, it looks like miniruby fails to require the stringio extension at install-time:

./miniruby -I./lib -I. -I.ext/common  ./tool/runruby.rb --extout=.ext  -- --disable-gems -r./x86_64-darwin16-fake ./tool/rbinstall.rb --make="/Library/Developer/CommandLineTools/usr/bin/make" --dest-dir="" --extout=".ext" --mflags="" --make-flags="" --data-mode=0644 --prog-mode=0755 --installed-list .installed.list --mantype="doc"
/Users/mistydemeo/oss/ruby/lib/rubygems/specification.rb:17:in `require': cannot load such file -- stringio (LoadError)
	from /Users/mistydemeo/oss/ruby/lib/rubygems/specification.rb:17:in `<top (required)>'
	from /Users/mistydemeo/oss/ruby/lib/rubygems.rb:1333:in `require'
	from /Users/mistydemeo/oss/ruby/lib/rubygems.rb:1333:in `<module:Gem>'
	from /Users/mistydemeo/oss/ruby/lib/rubygems.rb:116:in `<top (required)>'
	from ./tool/rbinstall.rb:24:in `require'
	from ./tool/rbinstall.rb:24:in `<main>'
make: *** [do-install-nodoc] Error 1

From looking in ext/stringio, stringio.a was built correctly, but maybe it wasn't linked properly.

I've attached the build logs, along with a script containing build steps to reproduce.