build failure on linux (x86_64-linux-gnu) platform

[allixx]

This conditional

ruby-packer/lib/compiler.rb

Lines 583 to 586 in 428dc24

	elsif `uname -m`.start_with?('x86_64')
	@utils.run(compile_env,
	'./Configure',
	'darwin64-x86_64-cc',

introduced by 2684a47 breaks compilation on linux platforms recognized as x86_64-linux-gnu.