puma: gem install --version 2.9.1 works, --version 2.9.2 and onward fails

This is a refined version of #625.

I can install v2.9.1 on my 'chine (OS X Yosemite 10.10.1):

gem install puma --version 2.9.1
Fetching: puma-2.9.1.gem (100%)
Building native extensions.  This could take a while...
Successfully installed puma-2.9.1
Parsing documentation for puma-2.9.1
Installing ri documentation for puma-2.9.1
Done installing documentation for puma after 5 seconds
1 gem installed

but v2.9.2 fails:

gem install puma --version 2.9.2
Building native extensions.  This could take a while...
ERROR:  Error installing puma:
    ERROR: Failed to build gem native extension.

    /Users/r/Developer/Chalcedony/usr/bin/ruby extconf.rb
checking for SSL_CTX_new() in -lssl... no
checking for SSL_CTX_new() in -lssleay32... no
*** extconf.rb failed ***
Could not create Makefile due to some reason, probably lack of necessary
libraries and/or headers.  Check the mkmf.log file for more details.  You may
need configuration options.

Provided configuration options:
    --with-opt-dir
    --with-opt-include
    --without-opt-include=${opt-dir}/include
    --with-opt-lib
    --without-opt-lib=${opt-dir}/lib
    --with-make-prog
    --without-make-prog
    --srcdir=.
    --curdir
    --ruby=/Users/r/Developer/Chalcedony/usr/bin/ruby
    --with-puma_http11-dir
    --without-puma_http11-dir
    --with-puma_http11-include
    --without-puma_http11-include=${puma_http11-dir}/include
    --with-puma_http11-lib
    --without-puma_http11-lib=${puma_http11-dir}/lib
    --with-ssllib
    --without-ssllib
    --with-ssleay32lib
    --without-ssleay32lib

extconf failed, exit code 1

Gem files will remain installed in /Users/home/sandbox/usr/lib/ruby/gems/2.1.0/gems/puma-2.9.2 for inspection.
Results logged to /Users/home/sandbox/usr/lib/ruby/gems/2.1.0/extensions/x86_64-darwin-14/2.1.0/puma-2.9.2/gem_make.out

I’ll poke around and try to understand what’s changed, but maybe someone else will recognize what’s going on right away.