Remove unnecessary linker flags

Cygwin/mingw linker should be able to link against shared library
itself.  Mswin build sets -def:$(DEFFILE) option by the default.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@66196 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

ext/bigdecimal/extconf.rb

@@ -1,10 +1,6 @@
 # frozen_string_literal: false
 require 'mkmf'
 
-def windows_platform?
-  /cygwin|mingw|mswin/ === RUBY_PLATFORM
-end
-
 gemspec_name = gemspec_path = nil
 unless ['', '../../'].any? {|dir|
          gemspec_name = "#{dir}bigdecimal.gemspec"
@@ -32,32 +28,6 @@ have_func("rb_rational_den", "ruby.h")
 have_func("rb_array_const_ptr", "ruby.h")
 have_func("rb_sym2str", "ruby.h")
 
-if windows_platform?
-  library_base_name = "ruby-bigdecimal"
-  case RUBY_PLATFORM
-  when /cygwin|mingw/
-    import_library_name = "libruby-bigdecimal.a"
-  when /mswin/
-    import_library_name = "bigdecimal-$(arch).lib"
-  end
-end
-
-checking_for(checking_message("Windows")) do
-  if windows_platform?
-    case RUBY_PLATFORM
-    when /cygwin|mingw/
-      $DLDFLAGS << " $(srcdir)/bigdecimal.def"
-      $DLDFLAGS << " -Wl,--out-implib=$(TARGET_SO_DIR)#{import_library_name}"
-    when /mswin/
-      $DLDFLAGS << " /DEF:$(srcdir)/bigdecimal.def"
-    end
-    $cleanfiles << import_library_name
-    true
-  else
-    false
-  end
-end
-
 create_makefile('bigdecimal') {|mf|
   mf << "GEMSPEC = #{gemspec_name}\n"
 }

ext/bigdecimal/util/extconf.rb

@@ -1,36 +1,20 @@
 # frozen_string_literal: false
 require 'mkmf'
 
-def windows_platform?
-  /cygwin|mingw|mswin/ === RUBY_PLATFORM
-end
-
-if windows_platform?
-  library_base_name = "ruby-bigdecimal"
+checking_for(checking_message("Windows")) do
   case RUBY_PLATFORM
   when /cygwin|mingw/
-    import_library_name = "libruby-bigdecimal.a"
-  when /mswin/
-    import_library_name = "bigdecimal-$(arch).lib"
-  end
-end
-
-checking_for(checking_message("Windows")) do
-  if windows_platform?
     if defined?($extlist)
       build_dir = "$(TARGET_SO_DIR)../"
     else
       base_dir = File.expand_path('../../../..', __FILE__)
-      build_dir = File.join(base_dir, "tmp", RUBY_PLATFORM, "bigdecimal", RUBY_VERSION)
-    end
-    case RUBY_PLATFORM
-    when /cygwin|mingw/
-      $LDFLAGS << " -L#{build_dir} -L.. -L .."
-      $libs << " -l#{library_base_name}"
-    when /mswin/
-      $DLDFLAGS << " /libpath:#{build_dir} /libpath:.."
-      $libs << " #{import_library_name}"
+      build_dir = File.join(base_dir, "tmp", RUBY_PLATFORM, "bigdecimal", RUBY_VERSION, "")
     end
+    $libs << " #{build_dir}bigdecimal.so"
+    true
+  when /mswin/
+    $DLDFLAGS << " -libpath:.."
+    $libs << " bigdecimal-$(arch).lib"
     true
   else
     false