Fix JRUBY-4962: "require 'pty'" fails with LoadError: no library spec…

…ified

with a little help from Wayne Meissner.

lib/ruby/site_ruby/shared/pty.rb

@@ -4,6 +4,7 @@ module PTY
   private
   module LibUtil
     extend FFI::Library
+    ffi_lib FFI::Library::LIBC
     # forkpty(3) is in libutil on linux, libc on MacOS/BSD
     if FFI::Platform.linux?
       ffi_lib 'libutil'
@@ -12,6 +13,7 @@ module LibUtil
   end
   module LibC
     extend FFI::Library
+    ffi_lib FFI::Library::LIBC
     attach_function :close, [ :int ], :int
     attach_function :strerror, [ :int ], :string
     attach_function :execv, [ :string, :buffer_in ], :int

test/test_pty.rb

@@ -0,0 +1,8 @@
+require 'test/unit'
+
+class LoadPtyTest < Test::Unit::TestCase
+  # JRUBY-4962
+  def test_require_pty
+    assert_nothing_raised { require 'pty' }
+  end
+end