[ruby-cvs:66274] usa:r59096 (trunk): Clear `DESTDIR` when running make

[usa at ruby-lang.org]

usa	2017-06-15 23:04:29 +0900 (Thu, 15 Jun 2017)

  New Revision: 59096

  https://svn.ruby-lang.org/cgi-bin/viewvc.cgi?view=revision&revision=59096

  Log:
    Clear `DESTDIR` when running make
    
    * spec/rubyspec/optional/capi/spec_helper.rb (compile_extension): `DESTDIR` is
      the drive letter of the ruby installed path as default on mswin, but not
      builddir of the ruby.  this causes spec errors if the drive letter is
      different in the installed path and builddir.

  Modified files:
    trunk/spec/rubyspec/optional/capi/spec_helper.rb