Can't set multiple flags in optflags

[djmarcin]

When trying to run:

RUBY_CONFIGURE_OPTS='optflags="-O3 -DRUBY_MARK_FREE_DEBUG=1 -DRGENGC_CHECK_MODE=2"' ./ruby-build 2.7.1 /home/vagrant/.asdf/installs/ruby/2.7.1

It fails with

configure: error: unrecognized option: `-DRUBY_MARK_FREE_DEBUG=1'

Debugging shows that the command line that ruby-build is trying to execute is

++ ./configure --prefix=/home/vagrant/.asdf/installs/ruby/2.7.1 'optflags="-O3' -DRUBY_MARK_FREE_DEBUG=1 '-DRGENGC_CHECK_MODE=2"' --enable-shared

I'm not sure why it is splitting the quoted arguments, but (at least in this case) it should not.

[hsbt]

#1758 may resolved this issue.