Pass ruby version build tag to go build and go test

Author: sue445

_gem/lib/go_gem/mkmf.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require_relative "util"
+
 module GoGem
   # Helper module for creating Go Makefiles
   module Mkmf
@@ -35,11 +37,13 @@ def $objs.empty?; false; end
 
       current_dir = File.expand_path(".")
 
+      goflags = "-tags=#{GoGem::Util.ruby_minor_version_build_tag}"
+
       File.open("Makefile", "a") do |f|
         f.write <<~MAKEFILE.gsub(/^ {8}/, "\t")
           $(DLLIB): Makefile $(srcdir)/*.go
                   cd $(srcdir); \
-                  CGO_CFLAGS='$(INCFLAGS)' CGO_LDFLAGS='#{ldflags}' \
+                  CGO_CFLAGS='$(INCFLAGS)' CGO_LDFLAGS='#{ldflags}' GOFLAGS='#{goflags}' \
                     go build -p 4 -buildmode=c-shared -o #{current_dir}/$(DLLIB)
         MAKEFILE
       end

_gem/lib/go_gem/rake_task.rb

@@ -3,6 +3,8 @@
 require "rake"
 require "rake/tasklib"
 
+require_relative "util"
+
 module GoGem
   # Provides rake tasks for `go test` with CRuby
   #
@@ -94,6 +96,8 @@ def initialize(gem_name)
     #
     # @return [Hash<String, String>]
     def self.build_env_vars
+      goflags = "-tags=#{GoGem::Util.ruby_minor_version_build_tag}"
+
       ldflags = "-L#{RbConfig::CONFIG["libdir"]} -l#{RbConfig::CONFIG["RUBY_SO_NAME"]}"
 
       case `#{RbConfig::CONFIG["CC"]} --version` # rubocop:disable Lint/LiteralAsCondition
@@ -123,6 +127,7 @@ def self.build_env_vars
       ld_library_path = RbConfig::CONFIG["libdir"].to_s
 
       {
+        "GOFLAGS"         => goflags,
         "CGO_CFLAGS"      => cflags,
         "CGO_LDFLAGS"     => ldflags,
         "LD_LIBRARY_PATH" => ld_library_path,

_gem/sig/go_gem/rake_task.rbs

@@ -28,7 +28,7 @@ module GoGem
 
     def initialize: (String gem_name) ?{ (RakeTask) -> void } -> void
 
-    def self.build_env_vars: () -> { "CGO_CFLAGS" => String, "CGO_LDFLAGS" => String, "LD_LIBRARY_PATH" => String }
+    def self.build_env_vars: () -> { "GOFLAGS" => String, "CGO_CFLAGS" => String, "CGO_LDFLAGS" => String, "LD_LIBRARY_PATH" => String }
 
     private