mkmf.rb: try_constant tests

* test/mkmf/test_constant.rb: tests for try_constant.
  TODO: define check_constant and use it.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38906 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
mkmf.rb: larger constants

* lib/mkmf.rb (MakeMakefile#try_constant): fix for larger constants.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38907 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
mkmf.rb: large unsigned

* lib/mkmf.rb (MakeMakefile#try_constant): fix for large unsigned.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38908 b2dd03c8-39d4-4d8f-98ff-823fe69b080e