extconf.rb fails automatically due to no detection of environmental make

[jashank]

I got some really quite surprising errors while trying to install leveldb-ruby:

> MAKE=gmake gem install leveldb-ruby
Building native extensions.  This could take a while...
ERROR:  Error installing leveldb-ruby:
    ERROR: Failed to build gem native extension.

        /home/jashank/.rvm/rubies/ruby-1.9.3-p194/bin/ruby extconf.rb
make: "/home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb/Makefile" line 18: Need an operator
make: "/home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb/Makefile" line 20: Could not find build_config.mk
make: "/home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb/Makefile" line 63: Missing dependency operator
make: "/home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb/Makefile" line 65: Missing dependency operator
make: "/home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb/Makefile" line 70: Need an operator
make: "/home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb/Makefile" line 82: Need an operator
make: "/home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb/Makefile" line 87: Need an operator
make: "/home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb/Makefile" line 172: Missing dependency operator
make: "/home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb/Makefile" line 194: Need an operator
make: "/home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb/Makefile" line 200: Need an operator
make: Fatal errors encountered -- cannot continue
make: stopped in /home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/leveldb


Gem files will remain installed in /home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15 for inspection.
Results logged to /home/jashank/.rvm/gems/ruby-1.9.3-p194/gems/leveldb-ruby-0.15/ext/leveldb/gem_make.out

Turns out, having gone bug chasing through rubygems, rbconfig and bundler, it's a bug in the extension -- the extconf.rb calls 'make', which is all well and good, except that isn't guaranteed to be GNU make on a *BSD system. Further, this doesn't honour the MAKE environment variable (or the --with-make-prog handle available from rbconfig).