Use create_go_makefile testdata

Author: sue445

ruby/testdata/example/ext/example/extconf.rb

@@ -3,38 +3,14 @@
 require "mkmf"
 
 ############ Appended for go native extension
-find_executable("go")
-
-# rubocop:disable Style/GlobalVars
-$objs = []
-def $objs.empty?; false; end
-# rubocop:enable Style/GlobalVars
-
+require "go_gem/mkmf"
 ############ Appended for go native extension
 
 # Makes all symbols private by default to avoid unintended conflict
 # with other gems. To explicitly export symbols you can use RUBY_FUNC_EXPORTED
 # selectively, or entirely remove this flag.
 append_cflags("-fvisibility=hidden")
 
-create_makefile("example/example")
-
 ############ Appended for go native extension
-case `#{CONFIG["CC"]} --version` # rubocop:disable Lint/LiteralAsCondition
-when /Free Software Foundation/
-  ldflags = "-Wl,--unresolved-symbols=ignore-all"
-when /clang/
-  ldflags = "-undefined dynamic_lookup"
-end
-
-current_dir = File.expand_path(".")
-
-File.open("Makefile", "a") do |f|
-  f.write <<~MAKEFILE.gsub(/^ {8}/, "\t")
-    $(DLLIB): Makefile $(srcdir)/*.go
-            cd $(srcdir); \
-            CGO_CFLAGS='$(INCFLAGS)' CGO_LDFLAGS='#{ldflags}' \
-              go build -p 4 -buildmode=c-shared -o #{current_dir}/$(DLLIB)
-  MAKEFILE
-end
+create_go_makefile("example/example")
 ############ Appended for go native extension